A lightning assault by the ISIS group that put the militants in control of a southern part of the Syrian capital killed 62 regime fighters, a monitor said Wednesday in a new toll.
ISIS launched the surprise attack on Monday night to seize the Qadam neighborhood of Damascus.
The Syrian Observatory for Human Rights war monitor gave an initial toll on Tuesday of 36 pro-government fighters dead, but said that loyalists had retrieved additional bodies since.
"The toll has risen to 62, most of them local pro-regime fighters," said the Observatory, a Britain-based monitor which relies on sources inside Syria for its information.
"Regime reinforcements have gathered on the outskirts of Qadam, but the operation to recapture it has not yet started," said monitor chief Rami Abdel Rahman.
ISIS have maintained a presence in parts of Damascus, including in the Palestinian camp of Yarmuk and the neighborhoods of Hajar al-Aswad and Tadamun.
It launched its Monday night attack from Hajar al-Aswad, taking advantage of a temporary power vacuum in Qadam after Islamist and jihadist fighters evacuated the area under a deal with the regime.
That agreement saw most of them head to the northwestern province of Idlib, which is controlled by a group led by Syria's former Al-Qaeda affiliate.
Al-Watan, a Syrian daily close to the government, also reported Wednesday that regime forces had sent reinforcements to Qadam, but said ISIS had only taken "a few buildings in the district's east".
ISIS swept across swathes of Syria and neighboring Iraq in 2014, but has since lost most of that territory to different offensives in both countries.
In Syria, the extremists only control less than five percent of the country, according to the Observatory, including in pockets in the eastern desert near the Iraqi border.
Fighters who pledged allegiance to ISIS are also present in the southern province of Daraa.
Syria's war has killed more than 350,000 people, starting in 2011 with the brutal repression of anti-government protests before spiraling into a complex conflict involving world powers and militants.