Gregg Zoroya

USA TODAY Opinion

At least 50 people were killed Sunday in a triple suicide bombing near the Syrian capital of Damascus as the United Nations special envoy launched indirect peace talks to end the country's civil war.

The bombing, which the Islamic State claimed it orchestrated, underscored the difficulty of finding a political solution to the war nearing its fifth anniversary.

The attackers detonated a car bomb at a bus stop, and two suicide bombers set off more explosives as rescuers rushed to the area, according to Syria’s state news agency SANA. The blasts went off in the Damascus suburb of Sayyda Zeinab, about 600 yards from one of the holiest shrines for Shiite Muslims.

The Syrian Foreign Ministry said more than 100 people were wounded in addition to the 50 killed.

State TV footage showed widespread damage that included several burning cars and a torched bus, plus blown-out windows and large holes in the facade of a nearby apartment tower, the Associated Press reported.

A website affiliated with the Islamic State, also known as ISIL or ISIS, said the attacks were carried out by members of the extremist group, which controls large areas in both Syria and Iraq.

The U.N.-hosted peace talks in Geneva got off to a rocky start Friday with U.N. Special Envoy Syria Staffan de Mistura meeting only with a Syrian government delegation, amid disagreement over which rebel groups should be allowed to negotiate. Opposition leaders refused to take part unless a siege of rebel-held areas was lifted, and Russian and Syrian bombardment of opposition fighters stopped.

De Mistura on Sunday paid an informal visit with the main opposition group — the Saudi-backed Higher Negotiations Committee — and said he is “optimistic and determined” about the talks, the AP said.

In Washington, Secretary of State John Kerry urged both sides Sunday to work toward a cease-fire and political transition for Syria. He said hundreds of thousands of Syrians remain trapped in cities where food assistance has not been allowed by the government of Syrian President Bashar Assad.

"Syria is an unfolding humanitarian catastrophe unmatched since World War II," Kerry said. "I appeal to both sides to make the most of this moment — seize the opportunity for serious negotiations."

The opposition group's spokesman, Salem al-Mislet, told the AP that the violence must stop before the talks can proceed. “It’s the duty of the responsibility of members of the (U.N.) Security Council to put the pressure on Russia to stop these crimes in Syria," he said.

Russia, a major Assad ally, began airstrikes in Syria in September.

Al-Mislet added, “It’s enough killing our children, killing civilians. They pretend to fight terrorism. In fact they don’t fight terrorism because they bring terrorism there and ISIS is spreading in many areas in Syria more than before because of these Russian strikes."

But the head of Syria's delegation in Geneva said the opposition is not serious about the talks.

“Those who speak about preconditions are coming to this meeting in order to derail it and is not concerned about a Syrian-Syrian dialogue,” Bashar Jaafari said, according to the AP. “With the opposition’s delegation not showing up, it shows that they are not serious and irresponsible at a time when Syrians are being killed.”