Protesters hold their party flags as they take part in an anti-U.S. rally in Karachi, Pakistan on Sunday, Jan. 15, 2006

Anti-American sentiment is running high in Pakistan, four days after a purported U.S. air strike killed at least 18 people in the country's remote tribal region. There has been no official comment from U.S. authorities, but Secretary of State Condoleezza Rice has promised to address Pakistani concerns over the attack.

U.S. Secretary of State Condoleezza Rice Monday defended U.S. anti-terror policy in Pakistan, but refused to comment directly on last Friday's deadly missile attack.

U.S. media report the CIA likely planned the mission, which hit a suspected al-Qaida safe house in Pakistan's remote tribal region near the Afghan border.

Pakistan has lodged a formal protest with the U.S. Embassy in Islamabad over the incident, and Rice promised to address Pakistani concerns.

Despite U.S. and Pakistani officials' efforts to play down the incident, Islamic groups in Pakistan are openly blaming the U.S., and vowed Monday to continue anti-American protests.

At least 5,000 people joined this demonstration in Karachi on Sunday. Similar rallies were held in major cities and villages across the country.

Officials from Pakistan's largest opposition party, the MMA, are also demanding that Prime Minister Shaukat Aziz cancel his planned trip to Washington, which begins Wednesday.

Mr. Aziz called the attack "regrettable" on Monday, but said his visit would proceed as scheduled.

Pakistani tribal villagers view damage caused by airstrikes in village of Damadola, near the Afghan border

Former Pakistani Senator Shafqat Mahmood says the missile strike has provided fresh ammunition for anti-American forces inside Pakistan.

"There's a fairly widespread resentment that Pakistan's territory has been violated by an ally," he said. "We've been strong supporters of the war on terror, and if your own territory starts to be hit, then it does create problems."

The attack occurred last Friday in the village of Damadola, about seven kilometers from the Afghan border. The tribal area is considered a relative safe haven for Taleban and al-Qaida insurgents.

Media reports have quoted anonymous U.S. and Pakistani officials as saying al-Qaida's deputy commander, Ayman al-Zawahiri, was expected to attend a dinner in Damadola on the night of the attack.

Officials here say the strike killed at least 18 people, but they believe Zawahiri was not in the compound during the attack. Local tribesmen claim the only victims were innocent civilians, including several women and children.

Pakistan has strongly condemned the attack and indicated that it came from the Afghan side of the border.

Meanwhile, Pakistani officials have also warned local tribesmen against harboring suspected militants.

Pakistan's information minister, Sheikh Rashid Ahmed, spoke to reporters in Islamabad a day after the attack.

"While this act is highly condemnable, we have been for a long time striving to rid our tribal areas of foreign intruders, who have been responsible for all the miseries and violence in the region," he said.

Pakistan has deployed some 70,000 troops to the region to secure the border and flush out suspected militants.