BEIRUT (AP) — Syrian rescuers say at least two ambulance workers and several other civilians, including children, have been killed in government airstrikes in the last rebel stronghold in the country’s northwest.

The Syrian Civil Defense, known as White Helmets, said Thursday’s airstrikes killed 16, including two ambulance workers in the town of Maarat al-Numan in Idlib province. The Britain-based Syrian Observatory for Human Rights said at least nine were killed in the airstrikes.

Syrian forces launched an offensive against the rebel-held territory in late April, leading to the collapse of a cease-fire negotiated by Turkey and Russia last year.

The violence has forced an estimated 330,000 people to flee their homes since May 1, moving toward the Turkish border, according to the United Nations. Several health facilities were targeted in the violence.