BEIRUT - Russian and Syrian government forces have been targeting hospitals as a strategy of war in Syria's conflict, according to a report released by a rights group Thursday.

Amnesty International said it has "compelling evidence" of at least six deliberate attacks on medical facilities in the Aleppo governorate over the past twelve weeks, which killed at least three civilians, including a medical worker, and injured 44 more. It said the attacks amounted to war crimes.

Aleppo witnessed some of the country's fiercest fighting in the buildup to the partial cease-fire that came into effect Friday as government forces backed by Russian airstrikes cut off a rebel supply route from Turkey.

A supply route to an opposition stronghold in the eastern part of Aleppo city remains open through another border crossing with Turkey, but it is far narrower and more dangerous than the one that used to run to the north.

Amnesty said the attacks on medical facilities aimed to pave the way for pro-government ground forces to advance on northern Aleppo.

On December 25, several missiles struck Baghdad Hospital in Hreitan, a town north of Aleppo City, killing a medical worker, and injuring 10 staff and 20 patients, a doctor and another medical worker told Amnesty International. It left the hospital in ruins.

Some of the last families remaining in Hreitan fled as pro-government forces advanced on the town in early February. "I have lived in Hreitan all my life, and I have never seen it deserted," said a father to Amnesty International. "The airstrikes destroyed the city's infrastructure including hospitals so there are no more services for us to be able to survive."

Russia has denied targeting civilians in its Syria campaign. Syria's president, Bashar Assad, has also denied targeting civilians, saying he is waging a war against terrorism, but he has said that it is a "rule of thumb" in war that innocent civilians die.

The monitoring group Physicians for Human Rights has documented 346 attacks against medical facilities in the course of the five-year conflict, killing 705 medical staff.

It said 315 of the attacks were conducted by Syrian or Russian forces. A report by the group last year said the Syrian government "systematically violated" the principle of medical neutrality by targeting medical facilities and doctors, detaining patients, and arresting, torturing, and executing doctors.