A British sniper has killed a senior ISIS fighter with a 'one in a million' night-time shot from nearly a mile away, it has been claimed.

The unnamed SAS marksman is said to have killed the terrorist with a 'head shot' close to the Syrian border having been given a window of just 15 seconds.

He is understood to be a sergeant with the SAS G-Squadron and a veteran of operations in both Iraq and Afghanistan, where he is said to have recorded as many as 100 kills.

A British sniper has killed a senior ISIS fighter with a 'one in a million' shot from a mile away using a US-made McMillan TAC-50 sniper rifle (as seen in this file picture), it has been claimed

According to the Daily Star Sunday, he is believed to have used a US-made McMillan TAC-50 sniper rifle as he targeted the fanatic from more than 1,500m away as he arrived at a safe house in a village.

The trooper is reportedly part of a counterterrorism drive in Iraq and Syria, which has been operating since the beginning of the year.

A source told the newspaper that the village in question was under ISIS control making a more preferable 'capture mission' impossible. The exact location has not been revealed.

The unnamed sniper is believed targeted the fanatic as he was arriving at a safe house in a village close to the Syrian border

'The SAS team had hoped that the ISIS commander would arrive during the day because a night shot was regarded as too dangerous,' the source said.

'But as evening approached the team realised that they were going to have to either abort or go for a night shot. The sniper said he wanted to take the shot and was given a "go order".'

The sniper had 15 seconds to take his shot as the extremist pulled up in a car. The source said the extremist was killed instantly after being shot in the back of the head.

The Ministry of Defence declined to comment when contacted by MailOnline this morning.