BEIRUT — Hezbollah fighters joined Syrian forces in battling rebels in a Damascus suburb that is home to a revered Shi’ite Muslim shrine, in a push to secure the area around the ornate, golden-domed mosque.
Protection of the Sayida Zeinab shrine has become a rallying cry for Shi’ite fighters backing President Bashar Assad, raising the stakes in a conflict that is increasingly being fought along sectarian lines.
The fighting in the area south of the capital is part of a wider military offensive by Assad’s forces to recapture suburbs held by rebels and areas in the country’s strategic heartland. Activists said violent clashes coupled with heavy artillery bombardment of the southern suburbs reverberated in the capital.
The main Western-backed opposition group, the Syrian National Coalition, warned of an impending humanitarian disaster.
It said regime forces, backed by Hezbollah and Iraqi Shi’ite fighters and dozens of tanks and armored vehicles, were besieging the area, trapping tens of thousands of civilians under heavy bombardment.
‘‘Civilians in this area live in grim fear and anxiety, with no electricity and no way to escape,’’ a statement issued by the group said.
The international community has been largely unable to end the Syrian civil war, now in its third year, which has killed 93,000 people, and likely many more, according to the United Nations.
President Obama, Russian President Vladimir Putin, and other leaders of the Group of Eight industrial economies meeting in Northern Ireland this week tried to narrow sharp differences between Russia, a key Assad backer, and Western leaders who support the rebels, but could not agree on whether Assad must go.
Obama last week authorized supplying rebel groups with weapons but has refused to describe the type of military support the United States will give the opposition. A French diplomat said Wednesday that officials from the United States and other countries in the so-called Friends of Syria group will meet in Doha, Qatar, on Saturday to respond to requests from rebel commander General Salim Idris, who has outlined urgent needs, including sophisticated weapons, the diplomat said.
Speaking in Berlin on Wednesday, Obama refused to be drawn about how the United States might supply the rebels.
‘‘I cannot and will not comment on specifics around our programs related to the Syrian opposition,’’ he said.
The Syrian war is increasingly pitting Sunni and Shi’ite Muslims against each other and threatening the stability of Syria’s neighbors.