Two suicide bombers struck close to the Syrian capital Saturday, killing at least 12 people and wounding dozens more in the latest attack to hit the predominantly Shiite area in recent months, state TV and an opposition activist group said.

The so-called Islamic State group claimed responsibility for the bombings through its Aamaq news agency, which said there were three attacks carried out by suicide bombers. Aamaq said two attackers were wearing explosive belts while the third was in a car.

Syrian State TV said the blasts in the Sayyida Zeinab area just south of Damascus killed 12 people and wounded 55 others. The Britain-based Syrian Observatory for Human Rights said 20 people were killed and dozens were wounded in the two explosions.

The suburb where the bombing took place is home to a shrine by the same name, one of the most renowned in Shiite Islam. The heavily guarded shrine to Sayyida Zeinab, granddaughter of Islam's Prophet Muhammad and the daughter of the first Shiite imam, Ali, receives thousands of Shiite pilgrims each year.

As The Christian Science Monitor's Emily O'Dell wrote in 2013:

When I first visited the shrine of Sayyida Zeinab in Syria right before the war broke out, I was struck not only by the shrine’s majestic mirror mosaics, towering marble columns, and golden dome, but also by the immense spiritual and communal power of the women – from all over the world – packed within its walls (not to mention the men praying outside of them). But now the shrine of one of Islam’s most revered women has become a prime target of Sunni rebel mortars. And with many Lebanese and Iraqi Shiite fighters killed in Syria being commemorated at home as “martyrs in the defense of the holy shrine of Sayyida Zeinab” – regardless of where they fought – the centrality of her symbolic presence in the conflict is clear. One senior Shiite cleric, Ali al-Amin, has decried the violence committed in her name: “Sayyida Zainab does not want bloodshed in the name of defending her shrine, but rather unity and shunning sedition.”

State TV aired footage from the blast site, showing several vehicles and shops on fire and at least two buildings whose balconies, doors and windows had been destroyed. Blood stains could be seen on the debris-covered road. Fire engines rushed to the scene to extinguish fires caused by the explosions.

State news agency SANA said the first blast was caused by a suicide attacker wearing an explosives belt, while the second was the result of a suicide attacker in a car rigged with explosives.

SANA quoted Prime Minister Wael al-Halqi as blaming the "brutal massacres" on Turkey, Saudi Arabia and Qatar, which are the main supporters of the Syrian rebels trying to remove President Bashar Assad from power.

Sayyida Zeinab has been a frequent target of bombings in Syria's civil war, now in its sixth year. On April 25, a suicide car bomb struck a military checkpoint, killing eight people, and in February, a series of blasts killed at least 83 people and wounded more than 170.

The blasts came as US-backed fighters in northern Syria tightened their siege on the IS stronghold of Manbij, where tens of the thousands of civilians are trapped by the fighting. The Syria Democratic Forces, a predominantly Kurdish group, encircled the town after capturing dozens of villages and farms near the Turkish border.

"The push toward Manbij slowed down because of fear for civilians there," said Mustafa Bali, a Syrian journalist who visited the front line. "All telecommunications with the town have been cut," he told The Associated Press by telephone.

The Observatory said tens of thousands of civilians in the town fear bombardment of residential areas at a time when most bakeries have stopped working and food is running out. It said airstrikes by the US-led coalition have killed 30 civilians, including 11 children, since SDF began its offensive on May 31.

Manbij, one of IS's largest strongholds in Syria's Aleppo province, is a waypoint on a key supply line between the extremists' de facto capital of Raqqa and the Turkish frontier.

In the central province of Homs, a 31-truck aid convoy from the International Committee of the Red Cross and the Syrian Arab Red Crescent entered the besieged town of Houla on Saturday, according to ICRC spokesman Pawel Krzysiek.

Krzysiek said the trucks are carrying food for 14,200 families as well as products such as mattresses, blankets, water pumps, hygiene kits, diapers and vaccines. In March, 28 trucks carrying relief entered Houla, he said.

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Earlier this week, the UN said the Syrian government had approved access to 15 of 19 besieged areas.

The UN estimates that 592,700 people live under siege in Syria, with about 452,700 of them under blockades by government forces. Lifting sieges on rebel-held areas was a key demand by the opposition during peace talks that failed earlier this year in Geneva.