Nigeria's President Olusegun Obasanjo has put security forces on high alert in the Niger Delta region after an attack on a key oil pipeline.
This man lost his six-month-old son to the blaze
He gave the order at a meeting with security and intelligence officials in the capital Abuja.
The apparent dynamite attack killed at least eight people and is expected to delay deliveries of more than 180,000 barrels per day for up to a week.
Pipelines have been attacked in the region a number of times before.
In other instances, pipelines have been cut by thieves to siphon off the oil.
Some local residents have long claimed they do not benefit from the oil wealth.
Mr Obasanjo's spokesman, Remi Oyo, said the president had ordered all defence and security personnel in the region to be placed in a state of high alert.
"We will not abandon this country to brigands. Criminals must be chased, caught and punished," the president was quoted in a statement as saying.
Wells shut down
The attack occurred 50km (31 miles) west of the oil centre of Port Harcourt, said Shell, hitting its Bonny terminal.
Andoni region local government chairman Monwan Etete said youths in four speed-boats had warned residents of local fishing villages to leave their homes shortly before the attack on Monday night.
He said 21 villages had been affected, and some of those killed were children.
A previously unknown militia group calling itself the Martyrs' Brigade has claimed responsibility for the attack.
After the incident, Anglo-Dutch Shell had to shut down two wells that supply the pipeline in the Niger Delta.
The company invoked "force majeure" to formally delay the shipments of oil. This is a legal term allowing a company to release itself from a contract due to unforeseen circumstances beyond its control.
Nigeria is the world's eighth largest oil producer, and the largest in Africa.