Two British Royal Air Force jets were scrambled from their base in Cyprus to urgently investigate Syrian planes that had crossed into international airspace.
The British Ministry of Defence (MoD) confirmed that unidentified planes legally crossed into Cypriot skies from the east of the country last Monday.
But it is understood the behaviour of the aircraft raised suspicions at RAF Akrotiri, less than 200 miles from Syria, prompting the rapid response.
The aircraft retreated before any action was taken.
Two Turkish F-16s are also believed to have been launched in support of the investigation from their base in Incirlik, Turkey.
A spokesman for the MoD said: “The MoD can confirm that Typhoon Air Defence Aircraft operated from RAF Akrotiri on Monday to investigate unidentified aircraft to the east of Cyprus; the aircraft were flying legally in international airspace and no intercept was required.”
It comes amid rising global tensions with Syria as the US seeks to build support for military strikes against President Bashar Asssad’s regime.
The Prime Minister's office indicated last week that Britain is not expecting its military bases such as RAF Akrotiri to be used by allies in any air strikes.
RAF Akrotiri is used by the RAF as a base for overseas operations in the Middle East and also for training.
On its website, the MoD says Typhoon Jets provide the RAF with a “multi-role combat aircraft, capable of being deployed in the full spectrum of air operations, from air policing, to peace support, through to high-intensity conflict”.