Syria's foreign ministry said Saturday that it would consider Turkish ground troops expected to temporarily monitor a safe zone deal in the country's northwest as "illegitimate".
The comments came a day after regime allies Russia and Iran agreed with opposition backer Turkey to jointly police a "de-escalation" zone in Syria's Idlib province.
Damascus's delegate to the talks, Bashar al-Jaafari, had described them as successful but the foreign ministry in Damascus on Saturday criticised Turkey.
"These agreements on de-escalation zones do not grant any legitimacy to a Turkish presence on Syrian territory," a source from the ministry told state news agency SANA.
"It is an illegitimate presence," the source added, while recognising that the accord "is temporary".
The Idlib zone is the fourth such area to be agreed among Turkey, Russia, and Iran after two days of talks in Kazakhstan aimed at easing the six-year Syria conflict.
Under the deal, a total of four de-escalation zones would be set up, each for a six-month period which could be renewed.
Three zones are already in place -- in Eastern Ghouta near Damascus, in central Homs, and in parts of southern Syria -- and are being monitored by Russian military police.
Idlib province, which lies along Syria's border with Turkey, was widely expected to be the most complex zone to establish.
Much of it is held by Hayat Tahrir al-Sham (HTS), an alliance of fighters dominated by Al-Qaeda's former Syrian affiliate.
In the Kazakh capital Astana on Friday, Turkey, Russia and Iran agreed "to allocate" their forces to patrol Idlib and parts of the neighbouring Latakia, Hama and Aleppo regions.
Turkey has long backed rebels in Syria's six-year conflict and intervened directly in August 2016 to fight the Islamic State (IS) militant group as well as Kurdish militias it sees as "terrorists".
Syria's government regularly complains about Turkey's intervention to the United Nations and says its military activities on Syrian soil constitute a violation of its sovereignty.
"The Astana deal is an international deal respected by Syria," Waddah Abed Rabbo, editor-in-chief of the Al-Watan daily, which is close to the government, told AFP.
"But it doesn't at all legitimise the presence of foreign powers -- Turkish or otherwise -- on Syrian soil without direct coordination with Syria's government," Abed Rabbo said.
More than 330,000 people have been killed and millions more displaced since Syria's crisis erupted in March 2011.