United Nations human rights chief Michelle Bachelet called on Friday for an immediate cessation of hostilities in Syria’s opposition-held Idlib province, saying the latest ceasefire attempt had yet again failed to protect civilians.

Turkey, which for years has backed Syrian rebels fighting to oust President Bashar al-Assad, agreed a truce with Russia that was supposed to have taken hold in the bastion of 3 million people in the northwest earlier this month.

“It is deeply distressing that civilians are still being killed on a daily basis in missile strikes from both the air and ground,” Bachelet said in a statement.

Her office received reports that air strikes resumed on January 15, she said. Armed groups had also carried out deadly ground-based attacks.

But witnesses and insurgent sources said pro-Assad Russian and Syrian jets have been hitting the province in a renewed assault. Moscow denied bombing civilians.

Since hostilities intensified in the so-called “de-escalation zone” in Idlib on April 29, U.N. monitors have verified incidents in which 1,506 civilians, including 293 women and 433 children, were killed, according to U.N. human rights spokesman Jeremy Laurence .