The RAF scrambled two Typhoon jets to intercept Russian planes near the UK's airspace, the Ministry of Defence (MoD) said.
The jets were scrambled from RAF Lossiemouth in Moray, Scotland, on Monday morning.
An RAF spokesman said: "We can confirm that quick reaction alert Typhoon aircraft from RAF Lossiemouth scrambled this morning.
"This is a live operation and therefore we will not be providing any additional information until the mission is complete."
The MoD has since confirmed the incident is now over.
The response to the quick reaction alert comes amid tensions between the West and Russia.
The RAF confirmed the Typhoons had taken off but the Ministry of Defence said it had not intercepted the Russian aircraft.
An MoD spokesman said: "We have got jets up in the air monitoring the situation but we have not intercepted anything."
The unidentified Russian plane was heading towards the UK from the north and had been monitored by NATO allies.
Russian activity close to the UK in recent months has led to several planes being scrambled and warships sent to monitor naval vessels.
HMS Westminster was reportedly tasked with intercepting two Russian warships and two supporting vessels as they passed close to British waters on 8 January.