Nigeria's government has ordered all oil firms that fled the Niger Delta in the wake of militant attacks to return to the area or cease operations.
Minister for Special Duties Godsday Orubebe said it was now safe for them to resume production.
But oil executives are sceptical about moving back and say the government cannot force them to return.
The announcement comes in a week when militants kidnapped a top politician's wife and blew up a major pipeline.
"There has been a great improvement in security in Port Harcourt in particular and within the Niger Delta in general"
The instability and violence in the southern region over the past four years have led to a significant drop in Nigeria's oil exports.
Many Nigeria-based oil firms have moved to the commercial capital, Lagos from Port Harcourt in the Delta.
Unemployment
"It is now time for these companies to return back and keep the productive wheel of the region busy again," Mr Orubebe said during a meeting with representatives of about 140 oil companies.
"We wish to state that there has been a great improvement in security in Port Harcourt in particular and within the Niger Delta in general."
The government will stop their operations if the orders are defied, he said.
However, some oil company officials, who spoke to the BBC's Fidelis Mbah in Lagos under condition of anonymity, dismissed the order as a political gimmick.
They said it was nearly impossible for the government to stop their oil exploration activities since they have not contravened any government law.
The oil companies say they cannot afford to risk their business interests and the lives of their workers because of the government's inability to check the activities of militants, our correspondent reports.
The minister said the location of offices from the Niger Delta had resulted in unemployment, which increased restiveness in the region.
Correspondents say most people in the Niger Delta live in poverty, the consequence of endemic government corruption.
The militants say they are fighting for a greater share of oil revenues for local people but many also have criminal motives.
They often abduct foreigners and prominent Nigerians who are usually freed after a ransom is paid.
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