BEIRUT (AP) -- An airstrike on a rebel training camp in northwestern Syria on Monday killed more than 50 Turkish-backed fighters and wounded nearly as many, a Syrian opposition spokesman and a war monitor said.
The airstrike in the northwestern part of Idlib province, the last rebel enclave in Syria, targeted a military training camp for Failaq al-Sham, one of the largest Turkish-backed opposition groups in Syria, said Youssef Hammoud, a spokesman for the groups.
The Britain-based Syrian Observatory for Human Rights, which monitors the war in Syria, gave a higher toll, at 78 fighters dead and nearly 90 wounded. Rescue missions were still underway, the Observatory said. It said it also suspected the airstrike was carried out by Russia, which is a close ally of Syrian President Bashar Assad in the country's civil war.
Leaders of the camp were among those killed in airstrike in Jabal al-Dweila, according to Hammoud. The camp is close to the borders with Turkey.
Syrian rebel groups vowed to retaliate.
"The factions of the National Front for Liberation we will respond to these violations," said Naji al-Mustafa, another spokesman for the Turkish-backed fighters, threatening to target government and Russian posts. He called it a "crime" by Russia.
Turkey and Russia had brokered a truce in Idlib earlier this year to halt a government offensive that displaced hundreds of thousands. But the truce remained shaky.
Turkey has long supported Syrian rebel forces in Syria. Russia has negotiated with Ankara to deploy observation teams in the rebel enclave to monitor the truce.
Last week, Turkish troops evacuated one of their largest military bases in the area, which was surrounded by Syrian government troops for months. Syrian opposition fighters said it was part of Turkey's redeployment of its forces in the shrinking enclave.