Syria's foreign ministry said Wednesday it was sceptical about Turkish efforts to fight the Islamic State group, in its first official reaction since Ankara began air strikes against the jihadists.
"It is better late than never, but are Turkish intentions to fight the terrorists of Daesh (IS), Al-Nusra Front, and Al-Qaeda-linked groups genuine?" the ministry asked in a letter to the United Nations.
"Or is it aiming to hit the Kurds in Syria and Iraq, maybe for other internal reasons?"
Turkey has conducted air strikes in Syria against IS since early Friday, after Ankara claimed a Turkish soldier was killed in cross-border fire by the jihadists.
The raids have also struck Kurdish militants in Iraq.
The ministry's letter made no direct mention of the strikes, but said that Syria "rejects the Turkish regime's attempt to paint itself as a victim that is defending itself", accusing Ankara of supporting "terrorist" groups.
Turkey also gave formal approval Wednesday for the United States to use a southern air base for raids against IS in Syria, after domestic and international criticism that it was not doing enough to curb IS activity along the border.
Syria's regime has repeatedly accused the Turkish government of supporting "terrorists" -- the word it uses to describe all armed groups opposed to Damascus.
"Syria has said for years that terrorism has no nation, religion or borders and warned terrorism's supporters that it would come back to them," the letter read.
"Unfortunately, we have lately begun to witness terrorism beginning to bounce back towards its supporters," it said.
The civil war raging throughout Syria began in March 2011 with anti-government protests, but has since devolved into a complex conflict.
The spectacular rise of IS prompted the US and its allies to begin an air campaign against the jihadist group in September 2014.