ANKARA/BEIRUT (Reuters) - Turkey promised on Saturday to do "whatever necessary" in response to Syria's shooting-down of a Turkish fighter, but did not immediately contest an assertion by Damascus that the jet had been in its airspace at the time. The downing of the aircraft, at a point close to the sea borders of both countries, provided a demonstration of Syria's formidable Russian-supplied air defenses; one of the many reasons for Western qualms about any military intervention to halt bloodshed in the country. Ankara's once-friendly relations with Damascus had already turned icy over President Bashar al-Assad's violent crackdown on a 16-month-old revolt, but signals from both sides suggested neither wanted a military confrontation over the incident. "It is not possible to cover over a thing like this, whatever is necessary will be done," Turkish President Abdullah Gul said, according to state news agency Anatolia, adding that Ankara had been in telephone contact with Syrian authorities.