ISTANBUL - Turkey scrambled fighters and briefly detained a Syrian passenger plane on Wednesday, suspecting it of carrying military equipment from Moscow, while Turkey's military chief warned of a more forceful response if shelling continued to spill over the border.Military jets escorted the Damascus-bound Airbus A-320, carrying around 30 passengers, into the airport in Ankara hours after Turkey's chief of staff said his troops would respond with greater force if bombardments from Syria kept hitting Turkish territory, Turkish state-run television said.The Turkish authorities had seized some of the cargo and the plane and its passengers would be allowed to continue their journey to Damascus, Davutoglu told reporters later, in televised remarks.He said Turkey was within its rights to investigate planes suspected of carrying military materials but declined to say what was in the seized cargo.Turkey would continue to investigate Syrian civilian aircraft using its airspace, Davutoglu said.He also said Syrian airspace was no longer safe and that Turkish passenger planes should not fly there. A Reuters witness at the border saw at least one passenger plane turn around as it approached Syria and head back into Turkey on Wednesday.Russia, from where the Syrian plane took off, is one of Syrian President BasharAssad's closest remaining allies and has blocked tougher UN resolutions against Damascus."Once a week a Syrian Airlines airplane flies from Moscow bound for Damascus," Interfax reported Vnukovo Airport spokeswoman Yelena Krylova as saying. "The plane took off normally, there were no incidents."Interfax cited her as saying 25 people were on board the chartered plane and it left 20 minutes after its scheduled afternoon departure time.Turkey's armed forces have bolstered their presence along the 900-km (560-mile) border and have been firing back over the past week in response to gunfire and shelling coming across from northern Syria, where Assad's forces have been battling rebels who control swathes of territory.Several mortar bombs landed outside the Syrian border town of Azmarin and heavy machinegun fire could be heard as clashes between the Syrian army and rebels intensified.Plumes of smoke rose into the sky and cries of "God is Greatest" rang out between the bursts of gunfire."We responded but if it continues we will respond with greater force," state television TRT quoted Turkey's Chief of Staff, General Necdet Ozel, as saying.NATO Secretary-General Anders Fogh Rasmussen said on Tuesday the military alliance had plans in place to defend Turkey."We are determined to control weapons transfers to a regime that carries out such brutal massacres against civilians. It is unacceptable that such a transfer is made using our airspace," Foreign Minister Ahmet Davutoglu said."Today we received information this plane was carrying cargo of a nature that could not possibly be in compliance with the rules of civil aviation," he said in Athens during an official visit, in comments broadcast live on Turkish television.