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.

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 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.