GENEVA (Reuters) - The humanitarian adviser to U.N. Special Envoy for Syria Geir Pedersen on Thursday regretted the collapse of a ceasefire in the northwest, saying that fresh violence threatens the lives of millions after more than 500 civilians were killed since late April.

Najat Rochdi, senior humanitarian adviser to Pedersen, noted the agreement between the United States and Turkey deal announced on Wednesday to set up “safe zone” in northeast Syria.

“Humanitarian actors are increasingly concerned by statements suggesting a possible military intervention, which would have severe humanitarian consequences in an area that has already witnessed years of military activity, displacement, droughts and floods,” she said in a statement.

(Story corrects headline and text to make clear statement from Pedersen’s adviser, not Pedersen himself)