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-Moussawi, an adviser to Prime Minister Nouri al-Maliki, told Agence France Presse.

Iranian President Mahmoud Ahmadinejad has urged a ceasefire in Syria and called for internal dialogue to resolve the crisis, but rejects a Turkish proposal to replace President Bashar Assad, Kuwait's press reported Thursday.

"The continuity of the fighting and the killing of innocent and unarmed Syrian citizens ... is unacceptable. A ceasefire must be achieved and then a dialogue started," said Ahmadinejad, cited by the daily Al-Anbaa newspaper.

Turkish artillery struck back at Syria on Wednesday after a Syrian mortar bomb landed on Turkish territory, local sources quoted by news agency Anatolia said.

Border troops in the Hatay province fired off a mortar strike at Syria, in retaliation for the Syrian bomb which struck Turkish territory at around 1315 GMT, the office of Hatay's governor said in a statement quoted by Anatolia.

Three Turkish soldiers and three Kurdish rebels were killed overnight after the militants ambushed a military post and a base in southeastern Turkey, the Anatolia news agency reported Wednesday.

The simultaneous attacks launched by Kurdish rebels near Cukurca in Hakkari province which borders Iran and Iraq triggered fighting that lasted until the early hours, Anatolia said, quoting a statement from the local governor's office.

Turkey's Kurdish rebels will retaliate to any Turkish attacks on Kurds in war-torn Syria, the second in command of the outlawed PKK said in an interview published Wednesday.

"Turkey should stay out of this conflict and stop its scheming," Murat Karayilan, who heads the outlawed Kurdistan Workers' Party (PKK) in the absence of its jailed leader Abdullah Ocalan, told Swiss daily Le Temps.

A senior U.S. official will hold talks in Ankara on Tuesday on a range of issues including the Syrian crisis amid heightened tensions between Ankara and Damascus, an embassy spokesman said.

"We continue to consult with our partners in the region including Turkey on a variety of issues related to Syria," U.S. embassy spokesman in Ankara T.J. Grubisha told AFP.

The United States on Monday called on all Syria's neighbors to keep a careful watch over their airspace, after Turkey said it had intercepted a Syrian plane from Russia carrying military equipment.

"Certainly we support the decision that Turkey has made in light of the apparent violation of their airspace by this aircraft," State Department spokeswoman Victoria Nuland told reporters.

Turkish Prime Minister Recep Tayyip Erdogan reiterated Monday that the cargo Ankara confiscated from an intercepted Syrian plane contained weapons, shrugging off Russian claims that the plane carried legal radar equipment.

"It is beyond any doubt that the cargo is war equipment," Erdogan told reporters in Ankara.

The majority of weapons secretly shipped to Syria at the behest of Saudi Arabia and Qatar go to hardline Islamic rebel groups rather than more secular organizations favored by the West, The New York Times reported Monday.

Citing unnamed officials, the newspaper said this was the conclusion reached in classified reports presented to President Barack Obama and other senior officials.

An Armenian plane ordered to land in Turkey Monday for security checks while en route to Syria's battered second city of Aleppo was allowed to resume its flight Monday after nothing suspicious was found, Anatolia news agency said.

"We know a plane from Armenia was forced to land in (eastern) Erzurum city... but it was allowed to resume its journey," the state news agency quoted Deputy Prime Minister Bulent Arinc as saying.