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Less than two hours later, police shot a suicide bomber near the Ninevah provincial government’s headquarters in Mosul, an al Qaeda haven in Iraq located 225 miles northwest of Baghdad. The bomber still managed to detonate his explosive belt, officials said, wounding two policemen.

The targeting of government offices is a hallmark of al Qaeda in Iraq, which may have sought to use Mr. Biden’s visit and the Independence Day holiday as a reminder of Iraq’s continuing instability.

Mr. Biden is keenly aware that Iraq’s security could crumble if formation of a new government results in alienating any of Iraq’s mainstream political groups. However, he pointedly did not meet with lawmakers aligned with anti-American cleric Muqtada al-Sadr, whose followers captured 40 of the 163 seats in parliament.

The United States does not consider the Sadrists a legitimate political entity, and Sadrists have long targeted American troops in Iraq.

Mr. Biden will meet Monday with Shiite cleric Ammar al-Hakim, leader of the Iraqi National Alliance, which has joined forces with Mr. al-Maliki, and with President Jalal Talabani, a Kurd.

Mahmoud Othman, a senior Kurdish lawmaker in Iraq’s parliament, said it was too soon to tell if Mr. Biden would be able to break the political deadlock.

“This will depend on to what extent the political parties will be flexible,” Mr. Othman said in an interview. “But if they stay adamant to their demands then, in my opinion, it will be hard to go forward.”