Syrian regime forces are engaged in fierce clashes with the rebels, who have been trying for years to break into the heart of Damascus. Both sides have confirmed their attendance at the next round of peace talks in Geneva later this week.
Syrian rebels attacked a regime-held area in northeastern Damascus on Tuesday for the second time in three days, rebels and regime media said.
Pro-regime media reported that rebels had launched a new offensive to regain ground they lost, saying they re-entered parts of the city's northeastern Jobar district in the east of Damascus.
A rebel spokesman confirmed the report: "At 5:00 am (0300 GMT) we launched the new offensive and we restored all the points we withdrew from on Monday. We have fire control over the Abassiyin garages and began storming it," Wael Alwan, a spokesman for the main rebel group, Failaq al Rahman, said.
The intensity of the regime's counterattack on Monday forced the rebels to retreat from most of the areas they captured that day in an industrial area that separated Qaboun from Jobar.
The regime said on Tuesday it was engaged in heavy fighting with "Syrian militants."
"They are encircled," the army said in a statement, without mentioning the Abassiyin area, where the rebels said they were fighting.
Syrian regime leader Bashar al Assad, along with allied Russian, Iranian and Shiite militia forces, have put rebels on the back foot with a steady succession of military victories over the past 18 months, including around Damascus.
For rebels, however, their first such large scale foray in over four years inside the capital signalled they were still able to wage offensive actions despite their string of defeats.
Russia deployed its air force in Syria in 2015 in support of Assad in his war against rebels battling to unseat him.
TRT World's Shamim Chowdhury has more from Turkish-Syrian border city of Gaziantep.
Geneva peace talks to resume
The United Nations said on Tuesday regime representatives and opposition rebels have confirmed their attendance at peace talks set to resume in Geneva on Thursday.
"All invitees who had already attended the previous round of talks in February 2017 have confirmed their participation," UN spokeswoman Alessandra Velucci told reporters.
United Nations' Special Envoy for Syria, Staffan de Mistura, who is trying to mediate a political agreement between the warring sides, is expected to visit Russia ahead of the talks.
Russia, Iran and Turkey brokered an uneasy ceasefire in Syria earlier this year.