Three British people and a Colombian working for oil giant Shell have been seized in Nigeria's Delta region.
Kidnappers snatched the four near the city of Port Harcourt, killing a Nigerian guard.
The oil-producing region is notorious for kidnappings by militants, who demand a greater share of its wealth.
But the Delta has been relatively calm since most major militant groups agreed to lay down their arms last year after the government offered an amnesty.
This is the first violent attack on foreigners in the region for many months.
The BBC's Caroline Duffield in Lagos says the amnesty is now drifting in the absence of President Umaru Yar'Adua, who is undergoing medical treatment in Saudi Arabia.
Gunmen snatched the four on Tuesday morning as they made their way to work at a power plant, police say.
Their police escort was shot dead and the driver is also believed to have been shot.
A Shell spokesman in Nigeria confirmed the attack.
"We are concerned for the safety of the contractor staff and our thoughts are with them and their families at this difficult time," he said.
The British Foreign Office said it was looking into the report "as a matter of great urgency".
No group has yet claimed to have kidnapped the group, which took place in Abia state.
Rivers State Police spokeswoman Rita Abbey told the AFP news agency that police had launched a search in and around the town of Aba, some 50km (30 miles) north-east of Port Harcourt.
Militants in the Niger Delta have cost Nigeria's oil industry millions of dollars over the years.
A variety of groups claimed to be fighting for the rights of local people to gain a greater share of the region's wealth.
But in reality, many of the groups stole oil from pipelines and extracted ransoms from kidnaps and used the money to arm themselves and finance more attacks.
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