BEIRUT - Fighters with the Islamic State of Iraq and Syria (ISIS) on Sunday 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 Britain-based Syrian Observatory for Human Rights, which has an extensive network of activists on the ground.

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

Get Breaking News Delivered to Your Inbox

ISIS supporters posted propaganda pictures claiming to show their 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. The extremist group has seized about one-third of Syria and neighboring Iraq over the past year.

Armed Islamic factions fighting forces loyal to Assad control parts of the Syrian capital and large parts of the city's suburbs. Earlier this year, ISIS fighters entered the Palestinian refugee camp of Yarmouk, east of Qadam, and control large parts of it.

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.