Two men suspected of terrorism and subject to stringent "control orders" have absconded and gone missing in Britain, according to media reports.
The reports said one man, accused of wanting to go to Iraq to fight, had been missing for two weeks after escaping from a London mental health unit, while another had disappeared some months previously.
The British Home Office and Scotland Yard would not confirm the reports and said they did not comment on individual control order cases.
Any breach of a control order would be dealt with on "a case by case basis", said a Home Office spokeswoman.
Last year's Prevention of Terrorism Act allows the Home Secretary to order suspects to be placed under control orders ranging from electronic tagging, surveillance and in extreme cases, house arrest.
The BBC said the man, who it said it could not name for legal reasons, had climbed out of a window from the mental health unit and was in his twenties.
It said he had been arrested in Pakistan last year where he was held for seven months before returning to Britain in January.
In March a control order was imposed, requiring him to report to police every day and surrender his passport.
The BBC said he was one of only six British citizens to be placed under such an order. His family was appealing for him to come out of hiding, the BBC said.