(DAMASCUS, Syria) — Airstrikes halted a Turkish military convoy carrying ammunition after it crossed into northern Syria on Monday, bound for a rebel-held stronghold, opposition activists said. The strikes hit near the highway where the convoy was moving, the activists added. It was not immediately clear whether it was Syrian government or Russian warplanes that struck near the convoy but the development marked a sharp escalation in tensions in the northwestern province of Idlib where Syrian troops have been on the offensive for weeks. Syria’s Foreign Ministry slammed Turkey, saying the convoy consisted of armored vehicles loaded with ammunition and was heading to Khan Sheikhoun, a major rebel-held town in Idlib province, the country’s last rebel stronghold. Turkey backs the rebels who have been in control of the region since 2012, while Russia backs Syrian President Bashar Assad’s government, which has vowed to take back Idlib.