At his swearing-in ceremony at the US embassy in Baghdad's Green Zone, Crocker said: "This government, under the leadership of Prime Minister Maliki, must continue to take the necessary steps to unify this country, and to deliver tangible improvements to the lives of all Iraqis."
Crocker's remarks came against a backdrop of continued violence in many parts of Iraq.
"The chances of success [in Iraq] are essentially zero because the Iraqi people have no voice"
Non Sequitur, Cadiz, Spain
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Five people were killed and nearly 20 others wounded in Thursday's biggest attack, when a car bomb exploded in the town of Mahmudiya, 30km south of Baghdad, police said.
In the capital, two policemen died when a car rigged with explosives and stuffed with a corpse blew up when they came to retrieve the body, a security official said.
Iraqi policemen found the car parked in al-Amel district of central Baghdad with a corpse inside.
When the policemen approached to examine the body, the vehicle exploded, killing two of them and wounding another six, the security official said.
Another two policemen were killed and two more wounded when armed men opened fire on the convoy of the chief of traffic police as it passed through a district of northern Baghdad near the Sunni al-Nida mosque, an official said.
Three more Iraqis were killed and another 20 wounded in a roadside bomb explosion in Baghdad's southwestern Baya district.
In Tal Afar on Thursday, the governor of Nineveh province acknowledged a setback to the authorities' efforts to deal with the surge in sectarian strife.
Hours after truck bombs killed 85 people in a Shia area of Tal Afar on Tuesday, up to 70 Sunni men were shot dead in a town which only a year ago was held up by George Bush, the US president, as an example of progress towards peace.
Durad Kashmula, the governor of Nineveh province, said on Thursday at a news conference in Mosul: "Yes, there are policemen who are involved.
"They have been arrested but released afterwards due to demonstrations and to deter strife," he said, referring to protests in Tal Afar on Wednesday.
However, Kashmula said they would be brought to justice in due course.
Brigadier Najim al-Jubouri, mayor of Tal Afar, which is close to the Syrian border and the regional capital Mosul, said on Wednesday that 18 people had been detained over the shootings. It was not clear how many remained in custody on Thursday.
Salih Qadu, head doctor of Tal Afar hospital, said the final toll from the two bombs on Tuesday was 85. He said 60 bodies of men shot in the aftermath had been brought to the hospital. A senior Iraqi army officer put the toll from those attacks at 70.
Kashmula said "hidden hands" were trying to stir up sectarian strife in Tal Afar, but he vowed to restore normalcy to the town, which has seen growing tension between Shias, Sunni Arabs and Turkish-speaking Turkmen.
At the international level, Vladimir Putin, the Russian president, on Thursday called for a deadline on the presence of foreign troops in Iraq in order to avert civil war.
Consultations with political and religious leaders were required, as well as "clear time limits for the foreign military presence in the country", Putin said in a statement sent to the Arab League summit in Riyadh.
|Residents of Mahmudiya mourn|
Thursday's deaths [Reuters]
he US senate could vote on Thursday on a war funding bill that includes a binding provision to withdraw US troops from war-torn Iraq, where more than 3,235 American soldiers have died, by March 31, 2008.
Bush reiterated on Wednesday his pledge to veto the legislation if it crosses his desk, but Democrats are pressing the president to sit down with legislators to find common ground.
Nancy Pelosi, the speaker of the House of Representatives, said: "Let us sit down together to do what is right for the American people, to address the war in Iraq, so that we can bring it to an end and bring our troops home safely and soon."