Iraqi President Jalal Talabani has criticised Syria for its support for a possible Turkish intervention against Kurdish rebels in northern Iraq.
Talabani says Arab unity must be preserved
Mr Talabani, himself a Kurd, said comments by his Syrian counterpart, Bashar al-Assad, represented "a dangerous crossing of red lines".
The Turkish parliament has authorised cross-border raids, but the government says action is not imminent.
Ankara blames the rebels for attacks on soldiers and civilians inside Turkey.
Both the US and Iraq have urged Ankara to avoid military action which they fear could destabilise the entire region.
The president of the Kurdish region in northern Iraq, Massoud Barzani, has rejected accusations that his government provides cover for Kurdish Workers Party (PKK) fighters.
Arab unity 'broken'
Mr Talabani's remarks were published in the pan-Arab daily Asharq al-Awsat on Saturday.
"President Assad's remarks are dangerous and run contrary to the spirit of Arab solidarity," the Iraqi president said.
"Usually I would refrain from commenting on Syrian positions in order to preserve our historic ties, but this time I am unable to support this dangerous crossing of red lines."
Mr Assad backed the Turkish threat during his visit to Ankara three days ago.
"It would have been better for him [President Assad] to say what the Americans and the Europeans have said, that it is better to adopt a political solution despite his understanding of the Turkish stance," Mr Talabani said in his interview.
The Turkish prime minister has renewed calls on Washington and Baghdad to take action against the fighters, threatening to authorise military action if they do not.
But there is still more time and room for diplomacy, says the BBC's Ian Pannell.
Ankara says PKK fighters attack Turkey from Iraq
Turkey is hosting an important regional conference on Iraq early next month and it is difficult to see how Ankara could order its troops across the border before this takes place, our Middle East correspondent says.
The PKK has been fighting for autonomy in south-eastern Turkey since 1984 and more than 30,000 people have been killed in the conflict.
The PKK has been labelled a terrorist organisation by Turkey, the US and the EU.