Islamic State (ISIS) militants severely damaged a 2,000-year-old temple in the ancient Syrian city of Palmyra Sunday, activists said.

The Britain-based Syrian Observatory for Human Rights, which relies on a network of informants inside the war-torn country, said the Bel Temple had been damaged, but did not provide further details. A Palmyra resident, who goes by the name of Nasser al-Thaer, told the Associated Press that ISIS militants set off a huge blast at 1:45 p.m. local time Sunday.

"It is total destruction," he said of the scene of the explosion. "The bricks and columns are on the ground."

"It was an explosion the deaf would hear," he added. Al-Thaer said only the outer wall surrounding the temple remains.

 The temple, consecrated to the Semitic god Bel, had been well-preserved and was a source of much pride for Syrians. It was consecrated in 32 A.D. It stood out among the ruins not far from the colonnades of Palmyra, which is affectionately known by Syrians as the "Bride of the Desert."

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The news of the latest destruction at Palmyra came just days after IS released propaganda images purportedly showing militants blowing up another Palmyra temple, the 2,000-year-old Baalshamin dedicated to the Phoenician god of storms and fertilizing rains.

The U.N. cultural agency UNESCO, which has designated Palmyra as a world heritage site, called the destruction of the Baalshamin temple a war crime. Earlier this month, relatives and witnesses said that ISIS militants had beheaded Khaled al-Asaad, an 81-year-old antiquities scholar who devoted his life to understanding Palmyra.

ISIS, which has imposed a violent interpretation of Islamic law across its self-declared "caliphate" straddling Syria and Iraq, says such ancient relics promote idolatry. It already has blown up several sites in neighboring Iraq, and it is also believed to be selling looted antiquities.

Earlier Sunday, ISIS fighters pushed into a large district in southern Damascus, clashing with rival militants just a few kilometers from the center of the Syrian capital, the extremist group and Syrian activists said.

More than two dozen militants were killed in the clashes on the edges of the Qadam neighborhood, said the Observatory.

The pro-ISIS Aamaq News Agency reported that ISIS fighters seized half of Qadam. The Observatory's Rami Abdurrahman said IS fighters were holding two streets and that fighting was continuing.

IS supporters posted propaganda pictures claiming to show ISIS fighters advancing in the narrow streets of Qadam. The authenticity of the images could not be confirmed independently.

ISIS has emerged as one of the most powerful forces in the battle to overthrow Syrian President Bashar Assad. Armed Islamic factions fighting forces loyal to Assad control parts of Damascus and large parts of the city's suburbs. ISIS fighters control large parts of the Palestinian refugee camp of Yarmouk, east of Qadam.

Also Sunday, a mortar round hit an upscale neighborhood of central Damascus, killing four people, including a girl, Syrian state TV said.

It is not uncommon for Damascus to be shelled. Sunday's attack targeted the posh neighborhood of Abu Rummaneh, which houses hotels and several embassies.

An Associated Press reporter on the scene saw two people wounded by shrapnel. Vehicles in the area were also damaged.

The Associated Press contributed to this report.