LONDON (Reuters) - British police investigating the attempted abduction of a serviceman from a Royal Air Force base in eastern England, said on Thursday they could not discount it being a terrorism incident.

The serviceman, aged in his late 20s, was jogging on Wednesday afternoon and not in uniform when he was approached by two men on a quiet, rural road near the married quarters of RAF Marham in Norfolk.

One of the men shouted at him and tried to pull him toward a car, police said. He fought off the attacker, knocking him to the ground, and the second man, armed with a what was believed to be a military-type knife, went to help his accomplice.

The married serviceman, who was very shocked but not hurt, ran off and the two attackers, described by police as being aged between 20 and 30 and of Middle Eastern origin in appearance, fled in the car.

Police said they had liaised with counter-terrorism officers but the motive remained unclear.

“We’re unable at this time to discount terrorism but I stress that other lines of inquiry are equally plausible and are being investigated,” Norfolk’s Assistant Chief Constable Nick Dean told a news conference.

RAF Marham is home to Britain’s Tornado GR4 Force which is involved in operations in the Middle East.

Britain is on its second-highest alert level of “severe,” meaning an attack is considered highly likely, with service personnel believed to have been the targets of a number of recent foiled plots.

In May, Junead Khan, 25, a supporter of the Islamic State (IS) militant group, was jailed for life for plotting to kill U.S. troops based in eastern England, while in April two Britons, inspired by IS, were imprisoned for planning to kill police and soldiers in drive-by shootings in London.

In 2013, British soldier Lee Rigby was hacked to death on a street in London in broad daylight near his barracks. Two British Muslims were later found guilty of his murder.

Dean said vigilance had been increased at Marham, which was hosting a families’ day event on Thursday, but the wider security threat to the public and military bases was unchanged.