Iraqi member of the parliament Ibrahim Bahr al-Uloum, center, salutes his colleagues after he was appointed the new oil minister during the National Assembly meeting

Iraq's parliament approved what was to be the final six ministers for the country's first democratically-elected government in the post-Saddam era. But one minister has declined to accept his post, leaving the Cabinet with a vacancy.

Approval of the final six ministers was to complete the long-awaited Cabinet, more than three months after historic multiparty elections. But the man slated to be human rights minister, a member of Iraq's Sunni minority, Hashem al-Shibli, said he was chosen for "sectarian" reasons and would not serve.

Four of the six Cabinet members approved are Sunni, including the man chosen by Prime Minister Ibrahim al-Jaafari to head Iraq's Defense Ministry, Saadoun al-Dulaimi. The vital Oil Ministry went to a Shi'ite ally of Mr. al-Jaafari, .

The prime minister expressed optimism that the formation of a diverse, multi-ethnic Cabinet will soothe deep divisions in the country.

Mr. Al-Jaafari said, "By endorsing the candidates, the National Assembly has achieved Iraq's unity. We have given more time for consultation and taken into consideration opinions and viewpoints of all Iraqi politicians for establishing a government with full portfolios comprehending all Iraqi spectra."

Violence has claimed some 300 lives in Iraq in the 10 days since the prime minister first announced his government selections. Sunday, gunmen killed an Iraqi transportation official in Baghdad. Elsewhere, U.S. military officials say coalition forces killed six insurgents and captured dozens more near Iraq's border with Syria. The U.S. military in Iraq also says coalition forces have captured a top aide to al-Qaida-linked terrorist Abu Musab al-Zarqawi.

In the United States, Michigan Democratic Senator Carl Levin said Iraq's new government will have to work hard to achieve and maintain unity. Mr. Levin spoke on ABC's This Week program.

"Disaffected Sunnis, who are now in the minority, are very worried about the Shia majority and what will be in the [future Iraqi] constitution, and whether that constitution will protect minority rights," he said. "And then you have the Shia who are in the majority and have been elected to run the assembly, and they want the power of a majority. I think there are some fundamental clashes politically. And that is just as big a challenge as the security situation is."

Appearing on CBS' Face the Nation program, the Republican chairman of the Senate Foreign Relations Committee, Richard Lugar, said Iraq's security situation will likely remain a serious challenge.

"The insurgents, who are apparently old Saddam types [loyalists], who really look for a military coup - for the overthrow of this fledgling government, are numerous enough to kill a lot of Iraqis," said Senator Lugar. "I think it is a terribly serious predicament."

Mr. Lugar emphasized the importance of training and equipping Iraqi security forces to combat the insurgency and eventually take over for coalition forces deployed in the country.