A wave of late night airstrikes pummeled the northwestern Syrian city of Idlib, killing at least 23 people, wounding dozens and trapping several under the rubble of their homes as the intense bombardment struck near two hospitals and a mosque, opposition activists said Tuesday.

At least seven children were among those killed, said the Britain-based Syrian Observatory for Human Rights, claiming that Russian aircraft carried out the strikes. Moscow, however, insisted it was not involved in the strikes on Idlib, a city held by several militant groups, including Al Qaeda's branch in Syria known as the Nusra Front.

"The Russian aviation hasn't performed any combat tasks, moreover hasn't conducted any airstrikes in the province of Idlib," the Russian Defense Ministry spokesman, Maj. Gen. Igor Konashenkov, said in a statement Tuesday.

Since the Russian military campaign began last September in an effort to shore up Syrian President Bashar Assad's forces in their battle against Islamic militants, Moscow has staunchly denied that its warplanes have hit any civilian areas in Syria.

Like its more powerful rival, the Islamic State group, the Nusra Front has also been excluded form a cease-fire brokered by Russia and the United States that went into effect in late February and collapsed weeks later.

The Nusra Front has evacuated all its civilian centers, such as religious courts, in the city of Idlib and nearby villages and towns, said an activist based in Idlib province who goes by the name of Ahmad Ariha.

"The Russians claim they are targeting the Nusra Front," said Ariha adding, that the air raids late Monday killed and wounded some 250 people. He said some of the casualties were taken to clinics near the Turkish border in the Bab al-Hawa area.

The Local Coordination Committees, another activist group that like the Observatory monitors the Syrian civil war, said the airstrikes hit two hospitals and one struck near a mosque. It said 50 people were killed and over 200 were wounded -- but different tolls are common in the aftermath of big attacks.

According to the Observatory -- which has a network of activists on the ground in Syria --  about 10 air raids targeted areas near the National Hospital, the Al-Jalaa public gardens and other neighborhoods in Idlib.

"The air raids either aim to pave the way for a ground offensive on Idlib or to make the resistance kneel," said Turkey-based activist Hassan Dughaim who is originally from Idlib and is in contact with residents in the province that border's Turkey. "Some people are fleeing the city but the bombing is chasing them. People are even getting bombarded in refugee camps."

Dughaim, the Observatory and the LCC all reported airstrikes on towns and villages near Idlib, in the province that carries the same name.

Ariha, the Syria-based activist, said fresh air raids on Tuesday destroyed two vaccination centers in the village of Kfar Takharim.

Amateur videos showed relief workers using flash lights as they dug through the rubble in the night. When a boy is seen being carried out alive from what appears to have been a building, screams of "God is great' could be heard in Arabic. Another video shows a man being carried into an ambulance.

The videos appeared genuine and corresponded to other AP reporting of the events depicted.