Turkey called on the UN Security Council to take "necessary action" to halt Syrian aggression against its territory after cross-border shelling killed five Turkish civilians.
In a sharp escalation of tensions between the neighbors, Turkey shelled Syrian targets in retaliation for the cross-border fire, the first to kill Turkish citizens.
"This is an act of aggression by Syria against Turkey," Ankara's UN Ambassador Ertugrul Apakan on Wednesday said in a letter to Guatemalan Ambassador Gert Rosenthal, who heads the rotating presidency of the 15-nation council.
"It constitutes a flagrant violation of international law as well as a breach of international peace and security. Turkey calls for an immediate end to such unacceptable violations."
The council was expected to issue a statement condemning the Syrian attack, UN diplomats said.
The incident, which Turkey said killed five women and children, was the most serious since June, when Syria shot down a Turkish fighter with the loss of its two-man crew and Ankara took the matter to NATO.
That same month, two Syrians in Turkey were killed by cross-border bullets.
"Turkey kindly requests for the Security Council to take necessary action to put an end to such acts of aggression and to ensure that Syria respects Turkey's sovereignty, territorial integrity and security," Apakan said.
But the council's member countries have been at loggerheads for months over efforts to curtail the brutal war raging in Syria since March 2011.
China and key ally Russia have vetoed three resolutions condemning President Bashar al-Assad's regime for its crackdown on dissent.
Earlier, Turkish Foreign Minister Ahmet Davutoglu expressed Turkey's "deepest concern" to UN chief Ban Ki-moon.
Davutoglu also spoke with Lakhdar Brahimi, the United Nations and Arab League peace envoy to Libya.
Ban encouraged Davutoglu to "keep open all channels of communication with the Syrian authorities with a view to lessening any tension that could build up as a result of the incident," spokesman Martin Nesirky said.
The UN chief also urged Damascus to "respect fully the territorial integrity of its neighbors as well as to end the violence against the Syrian people," Nesirky said.
"He calls on all parties to reduce tensions and to forge a path toward a peaceful resolution of the Syria crisis."
NATO and major Western powers condemned Damascus for the shelling, an attack the Pentagon labeled "depraved."
Since late July, Syrian rebels have seized control of at least three key border crossings with Turkey and others on the eastern border with Iraq.