BEIRUT: A Turkish drone strike Tuesday killed at least four people in a northeast Syrian city held by Kurdish forces, the latest in a flurry of attacks, a war monitor said.The Britain-based Syrian Observatory for Human Rights said the attack struck near a hospital in Qamishli, the defacto capital of a semi-autonomous Kurdish administration that runs large parts of the country’s northeast.The four victims, all affiliated with the administration, were killed while they dug trenches near Turkey’s border in anticipation of a new offensive that Ankara has threatened to launch since May, the monitor said.Ankara has launched successive military offensives in Syria. Most have targeted Kurdish militants that Ankara links to a group waging a decades-long insurgency against it.Turkey has stepped up its drone strikes in Kurdish-controlled areas of Syria since a July 19 summit with Iran and Russia failed to greenlight a fresh offensive, according to Kurdish officials and the Observatory.A Turkish drone strike on Qamishli at the weekend killed four people, including two siblings, said the Observatory.The Kurdish-led Syrian Democratic Forces have counted at least 13 of their members killed in several Turkish attacks since July 19.Syria’s conflict that began in March 2011 has killed nearly half a million people and displaced half the country’s pre-war population.