BAGHDAD — Iraqi lawmakers adjourned for the month Wednesday after failing to agree on a provincial election law, casting doubt on whether U.S.-backed balloting can be held in the country's 18 provinces this year.

The development is a setback to U.S. hopes for reconciliation among rival communities despite the decline in violence and comes after days of intense negotiations and heavy pressure from U.S. and U.N. officials.

Parliamentary speaker Mahmoud al-Mashhadani said the lawmakers will resume sessions on Sept. 9 but that he also has ordered a committee to continue negotiations over the provincial elections law.

The legislature also adopted a supplementary budget of $21 billion.

The decision to go into summer recess came after lawmakers failed to break a deadlock over Kurdish opposition to a power-sharing formula for the northern oil-rich city of Kirkuk despite days of intense negotiations and heavy pressure from U.S. and U.N. officials.

Officials involved in preparations for the elections — which the U.S. believes are necessary for national reconciliation — have said such a delay would likely push voting to next year.

Deputy parliamentary speaker Khalid al-Attiyah, however, insisted the provincial elections could be held this year as long as the legislation is passed in September.

Adoption of the elections law had been linked with the budget proposal, which needed to be approved before the lawmakers could adjourn, according to the constitution.

Parliament adjourned for the summer break last week but met four days in a special session to try to approve the budget and election bills.

Finance Minister Bayan Jabr has said passage of the supplemental budget would augment the overall budget by some $70 billion this year and is needed for food rations, fuel for power plants and raises for civil servants.

Approval of the budget measure came as U.S. lawmakers complained that the Iraqis were not paying enough for their own reconstruction.

A General Accounting Office report released Tuesday said Iraq could end the year with as much as a $79 billion budget surplus as oil revenues pile on top of leftover income the Iraqis still haven't spent on rebuilding.

The main sticking point on the election bill was Kurdish opposition to a plan that would equally divide the provincial council seats for Tamim province, of which Kirkuk is the capital, among Kurds, Turkomen and Arabs.

Kurds and their allies currently hold a majority on the council and fear a dilution of their power as they seek to annex the oil-rich area into their semiautonomous territory to the north.

Iraq's largest Sunni Arab party, the Iraqi Islamic Party, called for a vote on the measure to be delayed until after the monthlong summer break.

Meanwhile, a suicide car bomber rammed his vehicle into an Iraqi army patrol car in the northern city of Mosul, killing one civilian and wounding 10 people, including an Iraqi soldier, police said.

Iraqi army spokesman Maj. Gen. Qassim al-Moussawi told a news conference Wednesday that insurgents were carrying out attacks in Baghdad and elsewhere in response to a major U.S.-backed Iraqi offensive against al-Qaida in Iraq in Diyala province.

Defense Ministry spokesman Mohammed al-Askari announced separately that a weeklong general amnesty was being extended to those who agree to disarm in Diyala — a tactic that has been used by the Iraqi government in past operations.

U.S. military spokesman Brig. Gen. David Perkins said "security around the entire country of Iraq continues to improve, for the 11th straight week violence continues at the lowest level in four years."

Associated Press writers Bushra Juhi and Hamid Ahmed contributed to this report.