The Syrian army and rebels, including jihadist groups, fought in the capital Damascus and north of Hama on Thursday after the insurgents' biggest offensive for months, underscoring the bleak prospects for peace talks which resume later in the day.
The offensive seems unlikely to reverse 18 months of steady military gains by the government, culminating in December's capture of the rebel enclave in Aleppo, but it has shown the army's difficulty in defending many fronts simultaneously.
Increased fighting in recent weeks despite a ceasefire brokered in December by Russia and Turkey casts further doubt on peacemaking efforts in Geneva, where talks resume on Thursday after making little progress in recent rounds.
"We hope to see some serious partner on the other side of the table," Salem al-Muslet, spokesman for the opposition's High Negotiating Committee (HNC), said in Geneva.
Syrian President Bashar al-Assad's government, which is backed by Russia, Iran and Shi'ite militias, is also attending the Geneva talks. Both sides accuse each other of violating the ceasefire.
In Damascus, the intensity of clashes around the industrial zone in Jobar, on the edge of the central districts of the capital, increased after midnight, the Syrian Observatory for Human Rights, a Britain-based war monitor, reported on Thursday.
A military media unit run by the government's ally Hezbollah reported clashes early on Thursday in Jobar and a heavy bombardment aimed at rebel positions and movement in the area.
State TV showed a reporter speaking in the capital's Abassiyin district at morning rush hour, but the road appeared quiet with only one or two cars and a few pedestrians, and with the repeated sound of blasts in the background.
Near Hama, rebels spearheaded by the jihadist Tahrir al-Sham alliance, but also including groups fighting under the banner of the Free Syrian Army, made new advances overnight and fighting continued on Thursday, the Observatory said.
Rebels had gained control over 11 towns and villages in the first 24 hours of their offensive after it began late on Tuesday and advanced to within a few kilometers of the city of Hama, it said. On Wednesday, a Syrian military source said reinforcements were headed to the Hama front.
Tahrir al-Sham's strongest faction is the former Nusra Front group, which was al Qaeda's official affiliate in Syria until they broke formal ties last year.
Samer Alaiwi, an official from the Jaish al-Nasr FSA group, which is fighting near Hama, said on a rebel social media feed that the offensive was aimed at relieving pressure on rebels elsewhere and at stopping warplanes from using a nearby airbase.
"After the failure of political conferences and solutions, the military operation is an urgent necessity," he said