US Secretary of State John Kerry has told Iraqi Prime Minister Nuri al-Maliki that Iranian flights carrying arms to Syria through Iraqi airspace are "problematic", during an unannounced visit to Iraq.

A senior US official said the sheer number of overflights, which occur "close to daily", as well as overland shipments to Syria through Iraq from Iran, was inconsistent with claims they are only carrying humanitarian supplies.

"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."

- Secretary of State John Kerry

Kerry said that US politicians and the American people are watching what Iraq is doing and "wondering how it is a partner".

"Anything that supports President Assad is problematic," Kerry told reporters on Sunday.

"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 travelled from Jordan to Iraq after accompanying President Barack Obama to Israel and the Palestinian Authority.

He has urged Iraqi officials to stop overflights of Iranian aircraft carrying military personnel and equipment to support the Syrian government as it battles rebels.

Al Jazeera's Jane Arraf reported that an Iraqi official in the speaker's office, who asked not to be identified, said the US made it clear that Washington would insist that Baghdad fulfil its promise of searching Iranian flights bound for Damascus to make sure they were not carrying weapons.

Maliki had pledged to conduct regular searches of Damascus-bound planes last year. They searched two, including one returning empty from Damascus, before saying they did not have the capability to routinely check planes.

The overflights have been a source of contention between the US and Iraq and Kerry has told the Iraqis that letting them continue will threaten Iraq's stability, officials said.

The senior US official said it was in Iraq's interest to prevent the situation in Syria from deteriorating further, particularly as there are fears that al-Qaeda-linked groups may gain a foothold in the country.

'Unconstitutional' election delay

Kerry's visit also addressed democratic reforms and upcoming elections which are threatened by sectarian tensions.

The secretary of state has told Iraq's parliamentary speaker the US believes Iraq is facing a serious crisis and is in danger of going backwards, according to an official at the talks.

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Iraq's parliamentary speaker told Kerry that a decision earlier this month by the Iraqi government to postpone provincial elections next month in two Sunni-majority provinces due to security concerns is unconstitutional.

The statement said the speaker pointed out to Kerry that security during the last elections four years ago was much worse, and described the delay as a "political decision".

Following this discussion, Kerry says that Maliki agreed to revisit a cabinet decision to delay elections in two Sunni majority provinces next month.

The cabinet had agreed to delay the provincial elections after hearing that security forces could not protect voters in Anbar and Ninevah provinces, where Sunni residents have been protesting against the government since December.

Iraq's stability remains under threat largely due to rifts between the Shia-led government and Sunni politicians.

Sectarian differences have been growing wider even as the country marks the 10th anniversary of the US-led invasion, which ignited violence between Sunnis and Shia with the removal from power of Saddam Hussein, who was a Sunni.

Source: Al Jazeera And Agencies