US officials are questioning Iraq about Iranian flights in Iraqi airspace suspected of ferrying weapons to Syrian President Bashar Al Assad, whose conflict with rebels threatens to drag his neighbours into a regional struggle.

Three prominent US senators visiting Baghdad told Iraqi Prime Minister Nouri Al Maliki that ties with Washington would be damaged if his government permitted Iran to use its airspace to deliver arms to Syria.

One US official urged Baghdad to inspect the Iranian flights.

“This could really have some impact on Iraqi-US relations if it were true. The fact of the matter is they have the right to order a plane to land if they think they may be violating their airspace,” Senator John McCain told reporters.

McCain said Maliki told the visiting lawmakers he had still not received evidence of arms supplies that Iraq requested when US officials raised the Iranian flights earlier this year.

“If we make the allegation, I think is a legitimate request on his part to see the proof of it,” McCain said.

US State Department spokesman Patrick Ventrell said on Wednesday Iraq had a responsibility to continue with measures to prevent Iran shipping arms through its airspace.

“The easiest way, we think, is for them to require these aircraft to land and be inspected in Iraqi territory,” he said.

Iraq has had no real air force since the fall of Saddam Hussein and says it cannot defend its airspace. But Iraqi officials say they have no evidence that Iranian flights are carrying weapons or military hardware.

“The prime minister confirmed that Iraq’s stance is clear to not allow the passage of anything, of any weapon or anything linked to military activity,” said Ali al-Moussawi, Maliki’s media adviser.

“He is ready to follow up on any evidence.”

Meanwhile, a bombing in northern Iraq on Thursday killed the commander of a local police anti-terror unit, security and medical officials said.

Colonel Ismail Al Juburi, commander of the anti-terror squad in the town of Al Sharqat, was travelling to the provincial capital Tikrit when a magnetic “sticky bomb” attached to his car detonated, killing him and wounding his driver, a police lieutenant colonel and a doctor at Tikrit’s main hospital said.

The attack came a day after violence in northern Iraq killed three people - a female judicial investigator, a police sergeant and an anti-Qaeda militiaman.

Separately, Iraqi authorities laid the foundation stone for a cultural centre for the country’s dwindling Sabean population, at a ceremony in Baghdad on Thursday.

The $ 1.08 million project is expected to be completed by the end of the year, before Baghdad takes over as the 2013 Arab Capital of Culture.

The centre’s two-storey building in west Baghdad’s Qadissiyah district will include a museum, a multi-purpose hall and other unspecified facilities.

“This is a step towards restoring the liberty of this sect because they have been exposed to many injustices, like other minorities,” the deputy culture, minister Taher Nasser Al Hmoud said.

“We know that a lot of them left Iraq because of difficulties and terrorist activity against them, like other minorities. We are keen to maintain this minority, and we have to make them feel secure - emotionally, monetarily and physically.”

Also known as Mandaeans, Sabeans traditionally speak a variety of Aramaic, the language of Christ.