The death toll from overnight air raids on the Syrian city of Idlib has risen to 23 including seven children, an independent monitoring organization said on Tuesday.
"No less than 10 Russian airstrikes targeted the national hospital area in Idlib city" and other areas, the Syrian Observatory for Human Rights said in a statement.
The strikes on the north-western city, which is held by a coalition of mostly hardline Islamist rebel factions including al-Qaeda fighters, came five days after Moscow said it was suspending its strikes on Syrian militants.
Russia promptly denied that it had conducted any recent airstrikes in the area, and denounced media reports on the matter.
The Syrian military also uses Russian-made warplanes and weaponry, but activists say they can distinguish Russian planes by their sound and because they fly at higher altitude on bombing missions.
"We advise everyone to take a more critical attitude to any horror stories issued by the British tandem of the [London-based] Syrian Observatory for Human Rights and the Reuters news agency," Russian Defence Ministry spokesman General Igor Konashenkov said in comments carried by state news agency TASS.
The Defence Ministry previously said it would temporarily refrain from airstrikes to allow groups who signed up for a US- and Russian-backed cessation of hostilities a chance to cut their links with al-Nusra Front, the powerful Syrian branch of al-Qaeda.
Rebels have accused Russia of repeatedly targeting more moderate groups, while the United States has said that battlefield alliances between al-Nusra and other rebels have complicated implementation of the truce, especially around the key northern city of Aleppo.
Ten overnight strikes in Idlib hit areas around the National Hospital and other parts of the city centre, according to Rami Abdul-Rahman, head of the Syrian Observatory for Human Rights.
A volunteer with the White Helmets civil defence group confirmed that the strikes appeared to have been carried out by Russian aircraft.
Rescue workers were searching for survivors under the rubble of the bombed buildings, the volunteer, who asked to be known only as Majed, told dpa.
In the main rebel stronghold in the Damascus region, meanwhile, the Observatory and a local activist said that government advances were putting the area's food supply at risk.
Government forces on Tuesday captured swathes of vital agricultural land in the southern part of the Eastern Ghouta enclave, Abdul-Rahman said.
Rebels have been losing ground in the area recently after an outbreak of internal fighting between the powerful Army of Islam and rival groups including the al-Nusra Front.
The government has taken advantage of the infighting, sparked by a surge in assassinations over which the rival groups traded blame, to launch an offensive backed by intensified airstrikes.
Eastern Ghouta is strategically vital as it is the largest remaining opposition-held area in the Damascus region.
"Today we have lost lands which used to supply the area with vegetables... This is serious because vegetables were our main source of food supplies in the area," an activist in the area, who asked to be identified only as Baraa, told dpa by phone.
The Syrian conflict, which began with peaceful protests in March 2011, has spiralled into a multi-sided civil war that has cost some 250,000 lives and driven over half the country's population from their homes, according to UN estimates.