Iraq on Thursday refused to allow more than 120 Turkish buses to cross into Saudi Arabia, apparently loaded with Mecca pilgrims, because the passengers did not have visas issued by Baghdad, officials said.

"The government has decided to turn back 128 Turkish buses because they entered (Iraq) without following the procedures in force," Ali al-Mussawi, an adviser to Prime Minister Nuri al-Maliki, told AFP.

He said the vehicles had been stopped in preparation for their return to Turkey, without giving the number of passengers.

They entered the country through a border post in the autonomous Kurdish region in northern Iraq and were to have entered Saudi Arabia through the Arar post in the southwest of the country.

But the buses were not allowed through Arar because the passengers' visas had been issued by Kurdish regional authorities and not the central government, other officials said.

"Neither Ankara nor the Turkish embassy in Baghdad contacted Iraqi authorities about the arrival of such a large number" of people and "we don't really know if they are pilgrims," headed for Mecca in Saudi Arabia, said Mussawi.

"It's the first time this has happened."

A diplomat at the Turkish embassy, contacted by AFP, declined to comment.

Ties between Baghdad and Ankara have plummeted with Turkey refusing to extradite Iraqi Vice President Tareq al-Hashemi who has been sentenced to death in absentia and the two countries at odds over the Syrian conflict.

Baghdad also protested against an August visit to Kirkuk in northern Iraq by Turkish Foreign Minister Ahmet Davutoglu without the central government being informed in advance.