At least 19 rebels were killed in eastern Syria on Sunday in clashes for control of Deir Ezzor military air base, the Syrian Observatory for Human Rights said.
"The toll from the fighting is 19 martyrs," said the Britain-based monitor which relies on a network of activists and medics on the ground for its reports.
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The watchdog said there has been fierce fighting for the base for three days between rebels and regime troops backed by National Defence Force auxiliaries.
Observatory chief Rami Abdel Rahman said the rebels have succeeded in taking control of part of Al-Jafra village, a few hundred metres (yards) from the airport.
Residents of the village support the regime of President Bashar al-Assad, he said.