BEIRUT: The head of Syria’s main opposition group in exile called Sunday for international powers to impose a no-fly zone in border areas to protect civilians who are coming under increasingly intense attacks by regime warplanes and helicopters.

The president of the Syrian National Council, Abdelbasset Sayda, told the Associated Press that such a move by the international community would show President Bashar Assad’s regime that his opponents around the world were serious.

The Syrian opposition has been calling for a no-fly zone over Syria for months. But Sayda renewed the plea a day after U.S. Secretary of State Hillary 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 rebels.

“There must be special protection,” Sayda said by telephone.

Asked who would impose the no-fly zone, Sayda said: “We leave it to the international community.”

Russia and China have vetoed attempts to pass tough U.N. Security Council resolutions aimed at Assad’s regime. Last week, the U.N. and Arab League envoy to Syria Kofi Annan, announced his resignation following a frustrating six-month effort that failed to achieve even a temporary cease-fire.

Sayda said the no-fly zone should be along borders with Jordan and Turkey, adding that the opposition had called for such a move during last month’s Friends of Syria meeting in Paris attended by world powers.

Clinton told reporters after talks with Turkish Foreign Minister Ahmet Davutoglu in Istanbul Saturday that their countries needed to get into detailed operational planning on how to assist the rebels and said options could include imposing a no-fly zone over territory that Syrian rebels claim to control.

Washington sees Turkey as the key player both in supporting Syria’s opposition and in planning for what U.S. officials say is the inevitable collapse of the Assad government.

Clinton and other U.S. officials have in recent weeks cited rebel gains on the battlefield and the defection of senior Syrian military and political figures as signs that Assad’s rule is crumbling.

They have also highlighted rebel claims to control a “corridor” from Aleppo to the Turkish border as a potential future opposition safe haven.

But Clinton said Washington worried about other groups such as the Kurdish separatist Kurdistan Workers Party (PKK) or Al-Qaeda exploiting the chaos in Syria to gain a foothold.

Turkey this week accused Assad of supplying arms to the PKK, and Prime Minister Recep Tayyip Erdogan has raised the possibility of military intervention in Syria if the Kurdish threat increases.

The Kurdistan Freedom Hawks (TAK), a group connected to the separatist militant PKK, claimed responsibility Sunday for an attack last Thursday on a Turkish military bus that killed two soldiers.

Syria’s civil war has spread to almost every province in the country and the death toll has increased over the past weeks. Activists say more than 20,000 people have been killed since the revolt against Assad’s authoritarian rule began in March 2011.

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

The deaths of two Syrian journalists in Damascus Saturday were also reported Sunday.

The Observatory said that government forces were able to retake the northern town of Ariha, in the restive Idlib province, that had been under rebels’ control for months. The group said troops backed by tanks entered the town late Saturday and quoted witnesses as saying that many people had been detained and some had been the victims of “summary executions.”

Also Sunday, Syrian state news agency SANA said troops killed Wael Mohammad al-Majdalawi who is a leader of the Sunni group Al-Nusra Front, which claimed responsibility for deadly attacks over the past months including last week’s killing of a prominent Syrian television broadcaster.

In a video released Sunday, Capt. Abdul-Nasser Shumeir, who commands the rebel “Baraa Brigades” said government troops launched two attacks in an attempt to free 48 Iranians they have been holding for 10 days.

He said Assad’s regime is responsible for the safety of the Iranians, adding that any negotiations for their release should come after government forces lift the siege imposed on rebel-held areas.

He also called on the Iranian people to pressure their government to stop its support for Assad’s regime.

SANA also reported that security forces had 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.

The Observatory said three children, whose ages were between 6 and 11, were killed Sunday when a bus they were fleeing in with their parents from the Shammas neighborhood of the central city of Homs came under fire. It said government troops were conducting operations in the area.