BEIRUT - A hospital supported by Doctors Without Borders and specializing in pediatrics in a rebel-held northern Syria province has been destroyed in a series of airstrikes over the weekend that killed 13 people, including four staff and five children, the international medical charity said Monday.

The group, known by its French acronym MSF, said that two of four airstrikes directly hit the hospital in Millis, in the northern province of Idlib and put it out of service. Six other hospital staff members were wounded in the broad daylight airstrikes Saturday. The bombing of the hospital that serves as a reference center specializing in pediatrics also destroyed the operating theatre, intensive care unit, pediatric department, ambulances and a generator, the charity said. It was not clear which government had conducted the airstrikes and the MSF statement did not specify.

MSF said the hospital attack deprives 70,000 people in Millis and surrounding areas of essential medical care. The hospital, supported by MSF since 2014, used to receive 250 patients per day, many of them women and children

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"The direct bombing of another hospital in Syria is an outrage," says Silvia Dallatomasina, medical manager of MSF operations in northwestern Syria. She called for an immediate end to attacks on hospitals, pointing that four out of five UN Security Council members are participants in the war in Syria.

Hospitals, mostly in rebel-held areas, are regularly attacked. In July alone, the U.N. said it has recorded 44 attacks on health facilities in Syria. Syria's government and Russia, a major ally that has been carrying out airstrikes in Syria since September, deny targeting health facilities.

In recent days, a number of attacks were reported on medical facilities amid increased violence, and ultimately increased pressure on the health facilities, in northern Syria.

MSF said two facilities it supports in Idlib, controlled by insurgents, have reported nine mass-influxes of wounded in July, that left 466 wounded and 37 dead. In the first six-months of 2016, the same facilities reported only seven mass-influxes of wounded, with a total 294 wounded and 33 dead.