New air strikes on the town of Binnish in Idlib province in Syria's northwest have killed at least 14 people, Al Jazeera reported.
Fighting also appeared to continue on Tuesday inside and around the city of Aleppo, 50km from Idlib city, according to the British-based monitoring group, the Syrian Observatory for Human Rights.
Government forces and rebels in Aleppo had initially agreed on Monday to extend their truce for a second time, according to the army, as the United States and Russia vowed to "redouble" efforts to end the five-year conflict.
The cessation of hostilities was initially to last for two days but was later extended until Tuesday at 00:01 am (21:01 GMT Monday).
Announcing a further prolongation, the army command said: "The 'regime of silence' in Aleppo and its province has been extended by 48 hours from Tuesday 01:00 am (local time) to midnight on Wednesday."
The US and Russia also agreed to try extend a February 27 ceasefire across the whole of the country.
But Tuesday's deadly airborne raids, by either Syrian or Russian warplanes wounded dozens of other Syrians, the Observatory said.
A local rebel commander was also among those killed. There were no immediate details about other casualties.
Idlib province, which borders Turkey, is almost completely controlled by rebel groups, including the al-Qaeda-affiliated Nusra Front along with Ahrar al-Sham.
Washington and Moscow on Monday hailed some "progress" in reducing the fighting but admitted to ongoing "difficulties" in achieving a de-escalation in some areas as well as in ensuring humanitarian access to besieged areas.
On Sunday, Syrian rebels fired rockets into a regime-held district of Aleppo, killing five civilians including two children, the Observatory reported.
Elsewhere in Syria, calm returned to a prison after a deal was struck to end a week-long revolt by mostly political detainees.
Rami Abdel Rahman, head of the Syrian Observatory, said 83 prisoners held without charge have been released from Hama Central Prison since last week as part of the deal.
"The revolt has ended," he told Al Jazeera over the phone from the UK on Tuesday.
Hundreds of detainees revolted last week after five inmates were to be taken to the notorious Sednaya prison near Damascus so death sentences passed by an extra-judicial military tribunal could be carried out.
The Syrian Observatory said the Red Crescent was involved in brokering negotiations that led to the prisoners' release.
Inmates made appeals to the International Committee of the Red Cross after prison officials cut electricity and water amid food shortages and serious medical conditions among some of the inmates, the Observatory said.
Last week, sources inside the jail and the Observatory said government forces encircled the prison and fired tear gas as prisoners took captive the warden and several guards during heavy clashes.
"The UN Security Council has repeatedly demanded the release of all arbitrarily detained persons in Syria, but there has been no progress," a Human Rights Watch statement said.