Risk premiums for kidnap for ransom insurance or terrorism insurance will be reviewed across the north Africa region in light of the attacks, says Mr Robson.

CNN: Oil and gas industry reviews security

Malaysia's Sabah state shares a sea border with the southern Philippines, which is home to a number of Islamic militant and kidnap-for ransom groups.

BBC: Malaysia stand-off with Philippine group

Kidnap-for-ransom groups are prevalent in the southern Philippines, according to the BBC's Kate McGeown in Manila.

BBC: Abducted US teenager Kevin Lunsmann 'free' in Philippines

Sabah shares a sea border with the southern Philippines, which is home to a number of Islamic militant and kidnap-for-ransom groups.

BBC: Malaysia soldiers attack armed Filipino clan in Borneo

Local activists in the Niger Delta, which produces most of Nigeria's oil, regularly kidnap oil workers for ransom or smash installations, sometimes seriously cutting production.

ECONOMIST: Nigeria

Others suggest that Mr Reinhart did not have kidnap insurance, and so might have been personally liable for his employee's ransom.

ECONOMIST: Guerrilla tactics