The Turkish Foreign Ministry on Tuesday strongly condemned air strikes reported to have been carried out by Russian jets in the opposition-controlled northwestern Syrian city of Idlib late Monday.

In a news release, the Foreign Ministry said that the air strikes targeted a hospital and a mosque in the city, killing at least 60 civilians and injuring about 200. The ministry also called on the international community to act swiftly against what it called the "indefensible" crimes of the Russian and Syrian administration.

"It is obvious that Russia, which says that it defends a political solution in Syria and a ceasefire agreement, has careless trampled on these principles," the ministry said in its statement.

The Syrian Observatory for Human Rights said on Tuesday that Russian warplanes pounded Idlib overnight, killing 23 civilians in the heaviest strikes in months.

Dozens of civilians were also wounded in the raids, the monitoring group said.

"The air strikes are the most intensive on Idlib since the beginning of the truce," Observatory chief Rami Abdel Rahman reportedly said.

"Even though Idlib is not covered by the truce, it had been relatively calm with only intermittent raids," he added.

The Observatory said five children were among those killed in the strikes, which hit several residential areas and near a hospital and a public garden.

Footage posted on social media by the civil defense group known as the White Helmets showed rescuers holding the limp, dust-covered body of a small boy who was among the dead.

An AFP photographer saw medical staff helping crying children at a nearby clinic.

Russia, however, angrily denied its planes had conducted the air strikes."Russian planes did not carry out any combat missions, to say nothing of any air strikes, in the province of Idlib," Igor Konashenkov, a Russian Defense Ministry spokesman, said in a statement.

Russia launched its military intervention in Syria in September 2015 supposedly after a formal request by the Bashar al-Assad regime for military help.

In March, Russia decided to reduce its forces in the war-torn country.

According to a tally compiled by Turkey's state-run Anadolu Agency (AA), more than 361,000 people have been killed in Syria since the conflict erupted in 2011.