At least 31 people were killed across Syria on Sunday in a series of shootings, including fighting between gunmen believed to be army deserters and troops loyal to President Bashar Assad, a Syrian activist group said on Monday.

The Syrian Observatory for Human Rights said about half the deaths were in the city of Homs, where it said seven civilians were shot dead and another eight people were later killed in clashes between Syrian troops and suspected deserters.

The continued killing of civilians came as Syria warned countries on Sunday not to recognize a new opposition group, the Syrian National Council, threatening to take "strict measures" against any that did.

Foreign Minister Walid al-Moallem also responded to the attacks on several Syrian Embassies in Europe over the weekend, saying his government would not provide protection for diplomatic missions in Damascus belonging to countries that did not protect Syria's missions abroad.

A Syrian dissident on Monday criticized the foreign minister's threat to retaliate against any country that recognizes the opposition National Council.

"Moallem's statement is normal and shows that Syria is isolated," Ahmad Ramdan told Lebanese television.

"All countries in the world now treat the Syrian regime as an illegitimate, immoral and unconstitutional regime," he added.

Ramdan said the council will hold talks with European governments. "Contacts made by the council are being internationally welcomed. The council will be officially recognized by different countries in the coming weeks," he said.

Opposition groups formed the council earlier this month to be a united front against the regime of President Bashar Assad that has been cracking down on protests since March. More than 2,900 people have been killed according to a UN report.