Two RAF Typhoon jets were sent to investigate Syrian planes which crossed into international airspace, the Ministry of Defence has confirmed.
The MoD said the unidentified planes legally crossed into Cypriot skies earlier this week from the country's east last Monday. The planes are based at RAF Akrotiri, on the Mediterranean island's southern tip, 200 miles from Syria.
The aircraft retreated before any action was taken.
The Sunday Mirror quoted a military source as saying: "This is a clear sign of the tension boiling over because of Syria. Everyone is on edge.
"It is a pretty serious move to send up Typhoons - one of their roles is to intercept any possible enemy strike."
Two Turkish F-16s are also believed to have been launched in support of the investigation from their base in Incirlik, in southern 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."
The mission came as world leaders mulled intervening in the country riven by civil war.
The conflict, now in its third year, is fought between the government of President Bashar al-Assad and anti-government rebels, mostly from the disparate Free Syrian Army.
It has spilled periodically across Syria's borders with Lebanon, Iraq and Turkey, threatening to engulf the region. It has made almost two million refugees and last month the UN Secretary General Ban Ki-Moon said it has claimed more than 100,000 lives.
Number 10 indicated last week that Britain is not expecting its military bases such as RAF Akrotiri - a base for overseas operations in the Middle East and also for training - to be used by allies in any air strikes.