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
Mike Tindall has agreed a settlement with Express Newspapers over a story about his marriage to Zara Phillips.
The Met Office is warning of persistent heavy rainfall in western Scotland possibly leading to localised flooding.
The family of a World War One hero whose bravery won him a Military Cross have condemned thieves who stole the medal from a cathedral.