U.S. Vice President Joe Biden says "urgent assistance is clearly required" in Iraq, but he has not provided details on any U.S. aid.
Biden made the comment Tuesday during a stop in Brasilia, where he met with Brazilian President Dilma Rousseff. He also said Iraqis must "pull together" to end sectarian violence.
Meanwhile, Iraqi officials say at least 44 prisoners died in a militant assault on a prison in the city of Baquba.
Reports Tuesday differed as to whether militants or security officials killed the detainees. Morgue reports say the dead had close-range bullet wounds to the head and chest.
The French news agency AFP quoted a security spokesman for Prime Minister Nouri al-Maliki as saying the insurgents killed the prisoners while carrying out their attack late Monday.
Iraq's Shi'ite rulers defied Western calls on Tuesday to reach out to Sunnis to defuse the uprising in the country's north, declaring a boycott of Iraq's main Sunni political bloc and accusing Sunni power Saudi Arabia of promoting "genocide."
A push for political outreach
Washington has made clear it wants al-Maliki to embrace Sunni politicians as a condition of U.S. support to fight a lightning advance by forces from the Islamic State of Iraq and the Levant (ISIL) toward Baghdad, Reuters reported.
But the Shi'ite prime minister has moved in the opposite direction, announcing a crackdown on politicians and officers he considers "traitors."
On Tuesday, Maliki fired four top security officers for having "failed to fulfill their professional and military duties," Reuters reported, citing a government statement read on state TV.
The firings come a week after Sunni fighters took control of the northwest city of Mosul and several other cities.
Among those fired were Lieutenant General Medhi Sabah Gharawi, the top officer in Nineveh province where the militants gained ground, and commander Hidayat Abdulraheem, who fled a battle. The statement said a military court would try him in absentia.
Maliki also has lashed out at neighboring Sunni countries for stoking militancy.
The latest target of his government's fury was Saudi Arabia, the main Sunni power in the Gulf, which funds Sunni militants in neighboring Syria but denies it is behind ISIL.
"We hold them responsible for supporting these groups financially and morally, and for the outcome of that - which includes crimes that may qualify as genocide: the spilling of Iraqi blood, the destruction of Iraqi state institutions and historic and religious sites," the Iraqi government said of Riyadh in a statement, according to Reuters.
Maliki has blamed Saudi Arabia for supporting militants in the past, but the severe language was unprecedented.
On Monday, Riyadh blamed sectarianism in Baghdad for fuelling the violence.
Iraqi Army commanders insist they have regained the upper hand in the battle against Sunni militants in the Baquba area.
However, numerous eyewitness reports said the militants captured, at least briefly, parts of the town of Baquba, about 60 kilometers north of Baghdad.
Other reports said the nearby town of Mufraq was overrun by militants, who captured the police station as well.
Iraqi military spokesman Qassem Mohammed Atta told state TV that 52 prisoners inside the station's jail were killed in the attack.
Meanwhile, Iraq’s biggest oil refinery, Baiji, has been shut down and its foreign staff evacuated, refinery officials said on Tuesday, adding that local staff remain in place and the military is still in control of the facility.
The shutdown has led to parts of the country being deprived of fuel and power.
Eyewitnesses said Sunni militants captured the Qaim border post with Syria. Kurdish peshmerga fighters took the Yaroubia border post with Syria several days ago, after government forces reportedly fled.
UN leader urges dialogue
Earlier Tuesday, U.N. Secretary-General Ban Ki-moon urged al-Maliki to reach out to all factions and have a more inclusive approach to his government, amid a surge in violence by Sunni Islamist militants who have taken control of several Iraqi cities.
Ban, speaking to reporters Tuesday in Geneva, said he is very concerned about the rapidly deteriorating security situation in Iraq, including reports of mass summary executions by ISIL.
He said there is a real risk of further sectarian violence on a massive scale within Iraq and beyond its borders.
Ban said he spoke to al-Maliki, urging the prime minister to start an inclusive dialogue in search of a solution.
"Political instability often leads to a breeding ground of extremism and terrorism to infiltrate into society," Ban said.
"Therefore, I have been very urging and I am urging again that all the leaders in the world, they should really pay attention to the aspirations of the people before their aspirations or grievances are set into political instability," he added.
Ban said he would not predict whether the unstable situation in Iraq and in neighboring Syria, which is in its fourth year of war, could erupt into a regional war.
However, Ban told VOA he is concerned about the possibility of Iraq breaking up.
"What is important at this time is that the Iraqi government should have one state, whether it is a Sunni or Shi'ite or Kurds," Ban said. People "should be able to harmoniously live together, respecting and upholding human rights and values of the United Nations.
"I am very concerned about all these kind of situations that are happening here and there - in Africa, in Middle East and elsewhere," he said.
President Barack Obama said 275 U.S. military personnel will be sent to Iraq to help provide security to the embassy in Baghdad and U.S. personnel. The administration on Monday sought to reassure Americans that the deployment is not another open-ended commitment of troops to Iraq.
"This force is deploying for the purpose of protecting U.S. citizens and property, if necessary, and is equipped for combat," Obama said in a letter to lawmakers. "This force will remain in Iraq until the security situation becomes such that it is no longer needed."
Obama's notification to Congress Monday also said the move has the consent of the Iraqi government.
U.S. officials said 170 troops already are in Iraq, and about 100 more could be deployed as needed. Officials say the soldiers will help relocate some staff from the U.S. Embassy in Baghdad.
The embassy itself remains open.
Other options under consideration
While the president has ruled out sending ground forces back into Iraq, he met with his national security team Monday to consider other options.
They include possible air strikes against the Sunni militants, who already control large parts of northern Iraq and have vowed to seize Baghdad from the Shi'ite-led government.
The sudden advance by Sunni insurgents has the potential to scramble alliances in the Middle East, with the United States and Iran both saying they could cooperate against a common enemy, all but unprecedented since the 1979 Iranian revolution.
However, the Pentagon said it has no plans to enter into military cooperation with the Iranians in any action in Iraq.
Iran, the leading Shi'ite power, has close ties to al-Maliki and the Shi'ite parties that have held power in Baghdad since U.S. forces toppled Saddam Hussein in 2003.
While both Washington and Tehran are close allies of Baghdad, they have not cooperated in the past.
In a diplomatic rapprochement, U.S. ally Britain said it planned to reopen its embassy in Tehran, where a mob ransacked the mission in 2011.
A top State Department official said U.S. and Iranian diplomats met briefly Monday on the sidelines of nuclear talks in Vienna. The official said talks with the Iranians will not include any discussion of military coordination.
U.S. Secretary of State John Kerry told Yahoo News that the Iranians first have to be prepared to do something to respect Iraqi integrity and sovereignty before Washington makes a decision.
State Department spokeswoman Jen Psaki said this is not just a military challenge for Iraq's government. She said Iraqi leaders must make a sincere effort to govern in a nonsectarian manner and listen to the legitimate grievances of the Shi'ite, Sunni and Kurdish communities.
Iraq's Sunni minority bitterly complained that the Shi'ite government sidelined it and ignored its problems -- leading to terrorism and setting the stage for the current uprising by the militants.
Sunni involvement in ISIL
Sheikh Ali Hatem, who heads the influential Sunni Dulaim tribe, told Saudi-owned al Arabiya TV that "only 3 to 5 percent of Sunni fighters belong to ISIL."
Mosul Governor Athil Nujaifi argued several days ago that "many different Sunni groups" have joined together to fight the Maliki government.
Middle East analyst Nadim Shehadi of Chatham House in London said he cannot give an exact figure on the percentage of ISIL fighters battling the government, but he thinks that the "ISIL element is a small minority."
Shehadi said he thinks the current rout of government forces is due in part to the abrupt U.S. withdrawal from Iraq in 2011.
"This is in a way the result of the way the [U.S.] administration withdrew from Iraq. It created a vacuum. It was allied to (Sunni) tribesmen and fought the Islamic State of Iraq with them," Shehadi said.
"But then it abandoned the scene and they suffered from the policies of Maliki and they were in a way co-opted by the former Ba'athists, who also work with the Islamic State of Iraq,” he added.
Luis Ramirez contributed to this report from the White House. Lisa Schlein contributed to this report from Geneva. Edward Yeranian contributed to this report from Cairo. Some information provided by Reuters.