The head of Syria's main opposition group in exile has called for a no-fly zone in border areas to protect civilians. 

The president of the Syrian National Council, Abdelbaset Sieda, told The Associated Press on Sunday that such a move by the international community would show President Bashar Assad's regime that his opponents are serious. 

Sieda's statement came a day after U.S. Secretary of State Hillary Rodham Clinton said Washington and Turkey were discussing a range of steps including a no-fly zone over some parts of Syria as the regime increasingly uses its air force to attack rebel positions. 

"There must be special protection," he said. 

Asked who will impose the no-fly zone, Sieda said: "We leave it to the international community."

Activists reported more clashes in some Damascus suburbs, the battleground city of Aleppo in the north, central Homs province, and the restive southern town of Daraa. The U.K.-based activist group Syrian Observatory for Human Rights said it had no immediate reports of casualties.

Syrian state news agency SANA also reported that security forces ambushed an armed group in Aleppo and killed and wounded some of them. It said that al-Safira residents in Aleppo prevented gunmen riding in five cars mounted with machine guns from entering their area.

In Cairo, the Arab League said an emergency meeting of Arab foreign ministers on Syria that had been scheduled for Sunday in Saudi Arabia has been postponed. It did not say why the meeting was postponed or give a new date.

Two reporters killed

Also on Sunday two Syrian journalists were killed in the capital Damascus, according to reports on SANA and an Arab satellite television station.

SANA said one of its reporters, Ali Abbas, was killed at his residence by an "armed terrorist group" — the regime's catch-all term for its opponents — but gave no further details.

Pan-Arab satellite news channel Al-Arabiya television said that Bara'a Yusuf al-Bushi, a Syrian national and army defector who worked with the station and several other international news organizations, was killed in a bomb attack while covering a story in al-Tal, a suburb in northern Damascus.

Both reporters were reported killed on Saturday.

Journalists have suffered a number of casualties in the 17-month-old uprising against President Bashar al-Assad, and in recent months there have been several attacks on pro-regime media.

Activists say more than 20,000 people have been killed since the revolt began in March 2011.

Bombings in Damascus

On Saturday, two bombings in Damascus brought chaos to some of the capital's most exclusive areas in another symbolic blow to Assad.

One blast — from a device planted under a tree — was set off by remote control as a vehicle carrying soldiers passed by in the Marjeh district. The explosion, which caused no casualties, was about 100 meters from the Four Seasons, one of the top luxury hotels in Damascus.

After the blast, gunmen opened fire on civilians "to provoke panic," SANA reported.

At the same time, a second explosion went off near Tishrin Stadium, about a kilometre away, SANA reported.

Hours later, SANA said a bus was attacked in a Damascus suburb, killing six passengers traveling from the central province of Hama.

Explosions in the capital have become increasingly common as Syria's civil war escalates. On July 18, rebels carried out the deadliest bombing on a regime security building that killed four members of Assad's inner circle.