|Six people were killed in Qamishli as they attended the funeral of a Kurdish opposition figure on Saturday [YouTube]
Syria has warned it will retaliate against any country that formally recognises the recently-established Syrian National Council (SNC), which consists of groups opposed to President Bashar al-Assad's rule.
"We will take tough measures against any state which recognises this illegitimate council," Walid al-Moualem, the Syrian foreign minister, told a news conference broadcast by Syrian television on Sunday.
"We ... strongly condemn the attempts aiming to suppress the Syrian opposition and the increase in attacks targeting main representatives of the opposition"
- Turkish foreign ministry
The formation of the council has been welcomed by Western countries including the United States and France.
However, unlike the transitional council set up by Libyan fighters who overthrew Muammar Gaddafi, they have not offered it any formal recognition.
Meanwhile, activists in Syria have told Al Jazeera that heavy bombardment and artillery fire had been heard in a number of neighbourhoods in the city of Homs on Sunday.
The Local Co-ordination Committee said at least 18 people were killed in the country on Sunday. Among the dead were nine people in Homs and four from the same family in Damascus.
On Saturday, activists said security forces killed at least six people when they opened fire on tens of thousands of mourners at the funeral of a prominent Kurdish opposition figure.
Moualem described Meshaal Tammo as a "martyr" killed by "terrorists", suggesting he was targeted because he opposed foreign intervention in Syria. Tammo's family have blamed Syrian authorities for his death.
Tammo was expected to play a leading role in the SNC.
Moualem also criticised European countries, where he said Syrian embassies had been attacked by protesters, saying that if they did not meet their obligations to protect foreign missions, Syria would respond in a similar fashion.
He was speaking at a joint news conference with ministers from five Latin American countries, who were visiting Syria to show support for Assad's government.
Meanwhile, Turkey has condemned the assassination of Tammo as well as attacks against leading opposition figures in Syria.
"We ... strongly condemn the attempts aiming to suppress the Syrian opposition and the increase in attacks targeting main representatives of the opposition," the Turkish foreign ministry said in a written statement released late on Saturday.
Turkey is deeply sorry for the "loathsome assasination" of Tammo, as well as the wounding of prominent dissident Ryad Seif who was injured after being beaten on Friday in Damascus, the statement said.
"Turkey expects the Syrian government to realise as soon as possible that practices of violence aiming to suppress the Syrian opposition will not reverse the course of history," it said.
Tammo was gunned down on Friday in the northern town of Qamishli and his funeral became a mass rally with more than 50,000 demonstrators calling for the downfall of Assad's rule, activists have said.
Syria closed one of its border gates with Turkey and barred Turkish nationals from entering Syria following the bloody clashes in Qamishli, the Anatolia news agency reported.
Seif, a former legislator, had to be given hospital treatment after being beaten outside a mosque in the capital's commercial neighbourhood of Medan.
The United Nations human rights office said in a report issued on Thursday that at least 2,900 people have been killed in Syria since pro-democracy protests began there in mid-March.