Children stand near damaged vehicles as residents and soldiers loyal to Syria’s President Bashar al-Assad inspect damage after a suicide attack in Sayeda Zeinab.

A triple bombing killed at least 50 people in a predominantly Shiite suburb south of the Syrian capital of Damascus on Sunday even as a U.N. mediator held his first meeting with members of the main opposition group that seeks progress on humanitarian issues before it will join formal talks on ending the five-year civil war.

The attacks were claimed by militants from ISIS, and Syria’s delegate to the U.N.-sponsored peace talks said the violence confirmed the connection between “terrorism” and “some political groups” – a reference to those who oppose President Bashar al-Assad.

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

State TV showed several burning cars and a scorched bus, as well as blown out windows, twisted metal and large holes in the facade of a nearby apartment building. The golden-domed Shiite shrine itself was not damaged.

At least 50 people were killed, the Syrian Foreign Ministry said, with more than 100 wounded.

The suburb is one of the first areas where Lebanon’s Hezbollah group sent fighters in 2012 to protect it from Sunni extremists who vowed to blow up the shrine. Hezbollah and Shiite groups from Iraq are known to have fighters in the area.

The bombings cast a shadow over the Geneva talks, the first U.N. effort since 2014 to try to end the conflict that has killed at least 250,000 people, forced millions to flee the country, and given an opening to ISIS militants to capture territory.

Rocky start

The talks got off to a rocky start Friday when U.N. special envoy Staffan de Mistura met only with a Syrian government delegation. The main opposition group, the Saudi-backed Higher Negotiations Committee or HNC, boycotted the session, saying it won’t take part until preliminary demands are met: the release of detainees, the end of the bombardment of civilians by Russian and Syrian forces, and the lifting of government blockades on rebel-held areas.

On Sunday, de Mistura paid an informal visit to the HNC delegation, saying he is “optimistic and determined” about the talks.

HNC spokesman Salem al-Mislet told The Associated Press that the violence against civilians must stop first, saying the U.N. Security Council should put “pressure on Russia to stop these crimes in Syria,” he said. Moscow, which began its airstrikes in Syria in September, is a major Assad ally, along with Iran.

But Bashar Ja’afari, the head of the Syrian delegation, criticized the opposition in remarks to reporters.

“Those who speak about preconditions are coming to this meeting in order to derail it,” he said. “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.”

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