BEIRUT -- Turkey sharply escalated its confrontation with Syria on Wednesday, forcing a Syrian passenger plane to land in Ankara on suspicion of carrying military cargo, ordering Turkish civilian airplanes to stay out of Syrian airspace and warning of increasingly forceful responses if Syrian artillery gunners keep lobbing shells across the border.
Turkey's NTV television said two Turkish F-16 warplanes were dispatched to intercept a Syrian Air A-320 Airbus jetliner with 35 passengers en route from Moscow to Damascus, and forced it to land at Esenboga Airport in Ankara because it may have been carrying an arms shipment to the Syrian regime. Inspectors confiscated what NTV described as parts of a missile and let the plane resume its trip after several hours.
"There are items that are beyond the ones that are legitimate and required to be reported in civilian flights," Turkish Foreign Minister Ahmet Davutoglu said in remarks reported by the semiofficial Anatolia News Agency. "There are items that we would rate as troublesome."
There was no immediate comment from the Syrian side. Turkish transportation authorities earlier in the day said all Turkish aircraft should avoid flying over Syrian territory, possibly in anticipation of retaliatory action by Syria.
The steps taken by Turkey added ominous new tensions to its troubled relationship with Syria, where a nearly 19-month-old uprising against President Bashar Assad has evolved into a civil war and threatened to touch off a regional conflict.
Turkey is the host for main elements of the anti-Assad insurgency and for roughly 100,000 Syrian refugees, who have been fleeing in greater numbers as violence has increased along the 550-mile border in recent days. Several mortar bombs have landed on Turkish soil, prompting Turkish gunners to return fire.
News reports Wednesday spoke of intensified fighting close to the Syrian border settlement of Azamarin, with mortar and machine-gun fire clearly audible from the Turkish side.
Wounded civilians, some of them in makeshift boats full of women and children, could be seen crossing the narrow Orontes River, which demarcates part of the Syrian border with Hatay province in Turkey.
The Turkish chief of staff, Gen. Necdet Ozel, who visited parts of the border area Wednesday, was quoted by Turkish news media as saying military responses to Syrian shelling would be "even stronger" if the shelling persisted.
The rising tensions between Turkey and Syria are especially troublesome because Turkey is a member of NATO, which considers an attack on one member an attack on all.
On Tuesday, NATO Secretary-General Anders Fogh Rasmussen emphasized that NATO had "all necessary plans in place to protect and defend Turkey if necessary."