Airstrikes have hit hospitals in two locations in northern Syria – marking the latest in a series of attacks on medical facilities and workers in the five-year civil war.

Médecins Sans Frontières said eight staff members were missing after a facility it supports in Maaret al-Numan, Idlib province, was hit four times in two separate raids. MSF did not blame any side for the bombing, but there has been an unrelenting aerial bombardment by Russian warplanes and Bashar al-Assad’s regime in Idlib.

“This appears to be a deliberate attack on a health structure, and we condemn this attack in the strongest possible terms,” said Massimiliano Rebaudengo, MSF’s head of mission in Syria. “The destruction of the hospital leaves the local population of about 40,000 people without access to medical services in an active zone of conflict.”

In separate incident, Syrian opposition activists said a missile struck a children’s hospital in the rebel-held town of Azaz, near the Turkish border, killing 10 and wounding more than 30. The Turkish prime minister, Ahmet Davutoğlu, said a Russian ballistic missile had hit the town. Ankara shelled Kurdish positions near Azaz over the weekend.

Moscow’s intense airstrike campaign has helped Assad score his most significant advances since the beginning of the war, threatening to upend a “cessation of hostilities” deal agreed by major powers in Munich last week.

The Russian prime minister, Dmitry Medvedev, issued a blanket denial over the weekend that his country was targeting civilians and civilian facilities in Syria, but several attacks on health centres have been documented since Russia’s intervention. In the first month of the campaign launched last October, NGOPhysicians for Human Rights documented seven Russian attacks on medical facilities in Syria.

On Sunday, Riad Hijab, the head of the opposition’s high negotiations committee and a former Syrian prime minister, reiterated the opposition’s demand that airstrikes are halted and sieges around the country lifted, adding that Assad must leave for peace in Syria to take hold.

“Every day, hundreds of Syrians die from airstrikes and artillery bombardment, poison gas, cluster bombs, torture, starvation, cold and drowning,” said Hijab, speaking in Munich. “The Syrian people continue to live in terror and in utter despair after the international community failed to prevent even the gravest violations committed against them.

“The best approach to put an end to Daesh [Isis] and other extremist groups must start with the removal of the Assad regime.”

Russia resumed airstrikes on Monday in northern Latakia province near the Turkish border, bombing rebel positions to pave the way for a regime advance. The US president, Barack Obama, had urged Russia on Sunday to halt airstrikes against mainstream rebels.

Turkey, which strongly backs anti-Assad rebels, is fighting an insurgency by the Kurdistan Workers’ party (PKK) on its own territory, and has viewed with growing alarm what it sees as Kurdish expansionism in Syria. Ankara says the YPG is simply the Syrian affiliate of the PKK.

Turkey’s defence minister denied that Turkey had sent troops into northern Syria and said it had no intention of doing so, as speculation grows of a possible ground intervention by opponents of the Assad regime.

Saudi Arabia, the United Arab Emirates and Bahrain said last week that they wereready to send small numbers of ground forces into the embattled country as part of the US-led coalition against Isis.