BEIRUT — Syrian troops and rebels fought intense battles Thursday around a strategic air base in the country's north and a suburb of the capital that government forces have been trying to capture since last month, activists and state media said.

The fighting is part of the escalating violence in a Syrian conflict that the United Nations estimates has killed more than 60,000 people since the revolt against President Bashar Assad began in March 2011.

The Britain-based Syrian Observatory for Human Rights said rebels stormed parts of the Taftanaz air base in the northwestern province of Idlib before withdrawing. The state-run SANA news agency said government forces protecting the base "repelled the terrorists' attempt to attack the airport" and inflicted heavy losses.