BAGHDAD - Gunmen in northern Iraq killed a newly elected lawmaker from a Sunni-backed list that narrowly won Iraq's March elections, officials said, in a slaying certain to rattle the fragile political system.

There was no immediate claim of responsibility, but the Sunni lawmaker's allies in the Iraqiya coalition said Monday's shooting was politically motivated. His death, in the former insurgent hotbed of Mosul, was sure to further destabilize Iraqi politics, as the country's leaders continue to haggle over the makeup of a new government nearly three months after a parliamentary election.

A spokesman for the Iraqiya list said Bashar Mohammed Hamid Ahmed was killed in a drive-by shooting as he was on his way home, making him the first lawmaker to die since the March 7 election.

"We condemn this criminal act," said Osama al-Nujaifi, who heads the Iraqiya coalition in Ninevah province, where Mosul is located. "The motivation of this killing is purely political after the outstanding victory achieved by Iraqiya in the elections, and it is part of the vicious scheme carried out by some groups that want to keep anarchy in this country."

Iraqiya, headed by former Prime Minister Ayad Allawi, won 91 seats in parliament, in large part due to Sunni support in areas such as Ninevah.

Iraqiya narrowly beat a coalition led by Shiite Prime Minister Nouri al-Maliki, which won 89 seats. Because neither bloc won an outright majority, both are competing to form a governing coalition.

More than two months after the election, there are still no certified results. As the election impasse has dragged on, it has raised fears that the political fighting may spill over into violence on the streets.

Sunni officials have sometimes been targeted by insurgent groups, who see them as collaborators with the Shiite-backed government.

Mosul and other areas in Ninevah province are also at the center of a dispute between Kurds and Arabs. The Kurds say a large swath of territory from the Syrian to the Iranian borders should be part of their autonomous region; the Arabs argue it belongs with the rest of Iraq.

Those tensions have been particularly tense in Mosul, where Kurds have boycotted provincial council meetings for more than a year because they are demanding more representation on the elected body. U.S. officials have worried that the conflict could prove to be just as problematic as the Sunni-Shiite tensions so dominant in the rest of the country.

Meanwhile, an Iraqi election official said the election commission had received challenges to two lawmakers who recently won seats in the election, a development that threatens to extend a contentious process just as it looked as if the election impasse might be ending.

It was not clear why the challenges were being raised months after the election and after the candidates' names were first submitted to the election commission or whether the challenges, if approved, would alter the outcome of the vote. The electoral commission asked the Supreme Court to decide both cases and is awaiting a decision.