Police appealed for information and began an intensive nationwide search — but said he did not pose an imminent threat. Extra security measures at airports, including London’s Heathrow, led to delays.

Cmdr. Dominic Murphy, head of the Metropolitan Police’s counterterrorism command, told reporters that Khalife escaped Wednesday morning, wearing a prison kitchen uniform. The BBC reported, without indicating a source, that he may have strapped himself to the bottom of a delivery van.

Khalife has been charged, according to court documents reported by the Guardian, with a terror offense for eliciting or trying to elicit information on members of the British forces “which was of a kind likely to be useful to a person committing or preparing an act of terrorism,” and for a “bomb hoax” in January.

Authorities expressed concerns that he could try to leave the country. In addition to airport delays, the Port of Dover, east of London, announced enhanced checks “due to a police matter.”

Khalife has links to Kingston, southwest of London, according to a Metropolitan Police statement, and could have remained in London but “may have travelled further afield.”

“I also want to reassure the public that we have no information which indicates, nor any reason to believe that Khalife poses a threat to the wider public,” Murphy said. “But our advice if you do see him is not to approach him.”