Britons have been advised by the UK government to leave three states in Nigeria's oil-producing Niger Delta.
Nigerian militants have been responsible for kidnappings
In updates to travel advice on the Foreign Office website, citizens were warned that Bayelsa, Delta and Rivers States are unsafe.
The site states this is because of the very high risk of kidnapping, armed robbery and other armed attacks.
A Briton was one of four foreign oil workers kidnapped in Port Harcourt, capital of Rivers State, last week.
Since January last year, 31 British nationals and more than 180 foreigners have been kidnapped in the area. One Briton has been killed.
In its travel advice, the Foreign Office says British nationals who do stay in the region do so at their own risk.
It states this is because "of the very high risk of kidnapping, armed robbery and other armed attacks in these areas".
It also advises those who do stay in the three states that they are doing so "at their own risk" and says they should take professional security advice.
Most foreigners who go to the area, such as oil workers, already travel there with armed police escorts.
Recent attacks in the area have led to a 25% cut in Nigeria's oil production.
Those on ships and oil rigs off the coast of the Delta should also be aware of the "high risk of kidnappings and other armed attacks", the Foreign Office said.
Aberdeen North Labour MP Frank Doran, who has campaigned for tougher travel advice for oil workers travelling to the region, said the situation had become "very, very serious".
The UK government, the Nigerian government and private security firms could not guarantee the safety of Britons, he said.
He added: "I think the oil companies have to look seriously at whether or not they can continue to work there."
Oil company Royal Dutch Shell said it would support the relocation of its expatriate staff based in the Niger Delta who wished to leave.
In a statement it said: "The safety of our staff is our primary concern and we continually review our security measures and take a precautionary approach."