Syrian government forces and their allies have fought insurgents near Aleppo and jets carried out raids around a nearby town seized by Islamist rebels, a monitoring group says, despite international efforts to reduce the violence.
The United States and Russia, who support rival sides in Syria's civil war, said on Monday they would work to revive a February "cessation of hostilities" agreement which reduced fighting in parts of the country for several weeks.
But warplanes struck the town of Khan Touman, southwest of Aleppo, the British-based Syrian Observatory for Human Rights said. Rebels also fought government forces east of Damascus, and jets struck the rebel-held towns of Maarat al-Numan and Idlib.
A recent surge in bloodshed in Aleppo, Syria's largest city before the war, wrecked the 10-week-old, partial truce sponsored by Washington and Moscow which had allowed UN-brokered peace talks to convene in Geneva.
The talks, attended by government and opposition delegates including representatives from rebel groups, broke up last month with both sides accusing the other of killing the truce.
Russia and the US said in a joint statement they would step up efforts to convince the warring parties to abide by the ceasefire agreement.
"We have decided to reconfirm our commitment to the (ceasefire) in Syria and to intensify efforts to ensure its nation-wide implementation," they said.
"We demand that parties cease any indiscriminate attacks on civilians, including civilian infrastructure and medical facilities."
Russia's military intervention last September helped President Bashar al-Assad reverse some rebel gains in the west of the country, including in Aleppo province.
But insurgents captured the town of Khan Touman last week, inflicting a rare setback on government forces and allied Iranian troops who suffered heavy losses in the fighting.
Several Iranian soldiers were captured in the clashes, a senior Iranian lawmaker said on Monday.
Aleppo city is one of the biggest strategic prizes in a war now in its sixth year, and has been divided into government and rebel-held zones through much of the conflict.
The Observatory said warplanes struck rebel-held areas of the city early on Monday, and rebels fired shells into government-held neighbourhoods.
On the eastern edge of Damascus, government forces and their allies shelled rebel-held areas and clashed with insurgents in the area, the Observatory and the rebel force Jaish al-Islam said. Three people were killed and 13 wounded in air strikes on Idlib, it said.
The US-Russian joint statement said Moscow would work with Syrian authorities "to minimise aviation operations over areas that are predominantly inhabited by civilians or parties to the cessation".
It also said the two powers would press the rival parties to the conflict to ensure humanitarian deliveries to several towns which have been largely cut off by the fighting.