The Home Office is not confirming or denying whether any British workers have been involved.
But officials say they are investigating reports which suggest at least one Briton was taken when gunmen stormed a compound belonging to a Lebanese construction company in Nigeria.
ITV News reporter Sejal Karia talks from outside the Foreign Office:
More top news
Arkansas has become the first US state in 17 years to carry out back-to-back executions after putting two inmates to death.
Up to three million children risk going hungry over the school holidays, with increasing numbers of families relying on food banks, MPs say.
Tuesday will be a cold and windy day across the British Isles with a mix of sunshine and showers.