A fifth person, another child, was killed in a separate air raid by regime ally Russia also in the Idlib region, the Britain-based Syrian Observatory for Human Rights war monitor said.

The Idlib region is supposed to be protected from a massive regime assault by a September buffer zone deal, but the area housing three million people has come under increased regime and Russian fire since April.

The region is administered by Syria's former Al-Qaeda affiliate Hayat Tahrir al-Sham, but other jihadist and opposition factions are also present.

"Regime warplanes again targeted three hospitals in the south of Idlib," which had been hit and damaged in raids in previous weeks, the Observatory said.

There were no casualties in these raids on the village of Hass and the town of Kafr Nabl, it added.

Obeida Dandouch, who heads a rescue group in the area, said the strike in Kafr Nabl damaged a large part of what was still standing at the local hospital.

In May, Amnesty International accused the Syrian regime and Russia of launching "deliberate and systematic" assaults on hospitals in the northwest.

At least 25 hospitals and clinics have been destroyed or damaged by air strikes and shelling since the end of April, according to the United Nations.

Five rescuers were also killed in the last two weeks of June in air strike on the Idlib region.

Thursday's strikes killed four civilians, two of them children, in Kafr Nabl, Hass and the town of Khan Sheikhun in Idlib region, the Observatory said.

A Russian air strike near Al-Bara village killed a little girl and wounded several people, it added.

Syria's war, which started in 2011 with the brutal repression of anti-government demonstrations, has killed more than 370,000 people and displaced millions.