U.S. Secretary of State John Kerry pressed Iraqi Prime Minister Nuri al-Maliki on Sunday to stop Iranian flights over Iraq from carrying arms to Syria during a visit to the Iraqi capital.
Kerry also urged Iraq's Sunni Muslim, Shi'ite and ethnic Kurdish factions to commit to the political process as the country's precarious intercommunal balance comes under growing strain from the conflict in neighbouring Syria.
A U.S. official said earlier on condition of anonymity that Washington believes flights and overland transfers from Iran to Syria via Iraq take place nearly every day, helping President Bashar al-Assad crush a two-year-old revolt against his rule.
Kerry said he had "a very spirited discussion" with Maliki about the issue and he made clear U.S. unhappiness about the suspected arms transfers on Iranian flights through Iraqi airspace.
"Anything that supports President Assad is problematic," Kerry told reporters. "I made it very clear to the prime minister that the overflights from Iran ... are in fact helping to sustain President Assad and his regime."
Kerry's visit had not been previously announced to the public.
Speaking before the meeting, the U.S. official said Iraq had inspected only two flights since last July and that Kerry would argue Iraq did not deserve a role in talks about neighbouring Syria's future unless it tried to stop the suspected arms flow.
Iraqi officials denied allowing weapons to be flown from Iran to Syria through Iraqi airspace. Abbas al-Bayati, a member of the Security and Defence committee in parliament, said: "We have done our duty by randomly inspecting a number of Iranian flights and we did not find any leaked or smuggled weapons."
"If the U.S. is keen to push us to do more they have to give us the information that they have relating to this," he said.
At his news conference, Kerry said the United States had "agreed to try to provide more information" to the Iraqis and suggested that sentiment in the U.S. Congress may be turning against Iraq because of the suspected arms transfers to Assad.
Iraq's Shi'ite-led government says it takes no sides in Syria's conflict, but its interests are closely aligned with those of neighbouring Shi'ite Iran, a strong supporter of Assad.
According to reporters at a picture-taking session during Kerry's talks with Maliki, the U.S. diplomat appeared to joke that Hillary Clinton, his predecessor, had said Iraq would do whatever Washington asked.
"The Secretary told me that you're going to do everything that I say," Kerry said, according to the reporters.
"We won't do it," Maliki, also joking, replied, they said.
More than a decade after the U.S.-led invasion that toppled Saddam Hussein, Sunni Islamist militants linked to al Qaeda are regaining ground and the country's power-sharing government is all but paralysed.
Thousands of Sunni protesters have taken to the streets since December in protest against Maliki, and Kurdish lawmakers are weighing their options after the Iraqi parliament passed the country's 2013 budget without their participation.
"When consensus is not possible, those who are dissatisfied should not just walk away from the system, should not just withdraw, just as those who prevail should not ignore or deny the point of view of other people," Kerry said.
Kerry held talks with representatives of all three communities, including Osama al-Nujaifi, the Sunni speaker of parliament.
He also spoke by telephone to Massoud Barzani, president of Iraq's Kurdistan region, which is defying the central government in pressing ahead with plans to build an oil pipeline to Turkey that Washington fears could lead to the break-up of the country.
Sunni protesters accuse the Shi'ite-led government of marginalising their minority sect and using anti-terrorism laws to target them.
During his talks with Maliki, Kerry also asked the Iraqi prime minister and his cabinet to reconsider a decision to postpone local elections in two Sunni-majority provinces, Anbar and Nineveh, the U.S. official said.
The Iraqi cabinet last week postponed the votes, which were due on April 20, for up to six months because of threats to electoral workers and violence there - a step Washington believes will only increase tensions.
While violence has fallen from the height of the sectarian slaughter that killed tens of thousands in 2006-2007, Sunni Islamist insurgents have been invigorated by the increasingly sectarian civil war next door in Syria.
More than a dozen car bombs and suicide blasts tore through Shi'ite Muslim districts in the Iraqi capital Baghdad and other areas on Tuesday, killing nearly 60 people on the 10th anniversary of the U.S.-led invasion that ousted Saddam.
A statement released by Maliki's office following the talks said they had agreed on the need to find a political solution to the situation in Syria.
"The two sides also expressed concern at the development of events there (in Syria) and the urgency of working to contain it."
Separately, Kerry said U.S. President Barack Obama had described recent talks with Israeli and Palestinian officials as the most positive he had had to date, but that it would be "foolhardy" to express optimism considering that no negotiations are taking place.