Turkey has warned neighboring Syria that its military operations against civilians "must end immediately and unconditionally."
Turkish Foreign Minister Ahmet Davutoglu said this "is our final word to the Syrian authorities." He spoke to reporters in Ankara as the Syrian military was reported to be shelling residential areas in the port city of Latakia.
It was the third day of an assault against anti-government dissent there.
Syrian rights activists say the security forces have killed nearly 30 people in the coastal city since Saturday, including two on Monday. Witnesses in Latakia say people are trying to flee, but that several have been shot at checkpoints.
In Houla, a town near the city of Homs, activists say Syrian troops backed by tanks are carrying out raids and arrests.
Latakia and Homs are among the Syrian cities that have seen large protests demanding the resignation of President Bashar al-Assad.
The Turkish foreign minister visited President Assad in Damascus last week to urge an end to his brutal crackdown against the anti-government uprising. Mr. Davutoglu said Monday that unless the bloodshed ends immediately, there will nothing left to discuss with Syrian authorities.
A U.N. agency says the shelling of Latakia has forced about 5,000 Palestinians to flee a refugee camp in the southern part of the city. The U.N. is expressing concern about the situation.
Activists and witnesses say Syrian gunboats joined tanks in firing on Latakia Sunday, a new element in the government's crackdown that has been escalating since mid-March.
Syrian officials have given a different account of events in Latakia. They deny the city was shelled from the sea, and say that naval vessels were on routine duty to protect the coast and prevent arms smuggling.
On Sunday, Syria's state-run news agency said law enforcement personnel were pursuing gunmen who it said were terrorizing residents of Latakia.
Details of events in Syria are difficult to verify independently because the government allows very few foreign news reporters into the country and restricts their movements.
Rights groups and activists say at least 1,700 people have been killed since the start of the government's crackdown.