Oil company Royal Dutch Shell says it has temporarily stopped production at its main offshore oilfield in Nigeria, following a militant attack.
The raid took place overnight on the Bonga oil platform about 120km (75 miles) off the coast of the Niger Delta, the company said.
It is the first attack on the oilfield, which normally produces about 200,000 barrels a day.
Attacks in the inshore Niger Delta have helped drive up the world oil prices.
Nigeria's valuable offshore oilfields had always been considered difficult for most militants to attack, the BBC's Alex Last reports from Lagos.
But for the first time in the early hours, gunmen in boats reached the Bonga installation, Shell's flagship project.
A Nigerian navy spokesman confirmed reports that militants had kidnapped a US captain from a separate vessel on their way back from the attack.
Sophisticated
The gunmen failed to get inside the platform, but attacked a key vessel used for production storage and offloading, a Shell spokesman said.
Several people were reported to have been injured.
Militants from the Movement for the Emancipation of the Niger Delta (Mend) claimed the attack, the Associated Press news agency reported.
Mend says it is campaigning for a greater share of the region's oil wealth to be kept by local people, but the government says they are criminals motivated by the ransoms they receive from oil companies.
The shutdown has cut a tenth of Nigeria's total output in one go.
This comes on top of a reduction of at least 20% in recent years following inland attacks.
Our correspondent says Bonga was new, expensive and working well despite the difficulties and repeated attacks affecting the company's inshore operations in the Delta.
The militants in the Delta are getting more sophisticated and better equipped and armed, he says.
Now they have proven that in terms of distance at least, all of Nigeria's facilities are within their reach.
So, 200,000bbl/day gone, that neatly balances out the Saudis' planned rise in production in July.
It should bring oil up over $140/bbl on the markets tomorrow.
Looks like Brent and other prices spiked up over $4 but have started falling again.
Hard to know what 'damage to a vessel' means. The fact that prices are not rising further suggests the damage is not that great and that they will be up and running again within days? Who knows..
Indeed, they're vague about the damage, but that's SOP for the corporate types.
The thing is that even if there's no significant damage, it raises the cost of operations for the company. If you were an oil engineer, would you want to work in the Niger Delta where you might be killed or kidnapped? So then they have to offer higher wages, more security, more bribes to the local police and army, and so on.
And this increased production cost gets passed on to others...
Not ANZ-specific except in likely effect on oil prices, but...
Nigerian attack closes oilfield
So, 200,000bbl/day gone, that neatly balances out the Saudis' planned rise in production in July.
It should bring oil up over $140/bbl on the markets tomorrow.
Looks like Brent and other prices spiked up over $4 but have started falling again.
Hard to know what 'damage to a vessel' means. The fact that prices are not rising further suggests the damage is not that great and that they will be up and running again within days? Who knows..
Indeed, they're vague about the damage, but that's SOP for the corporate types.
The thing is that even if there's no significant damage, it raises the cost of operations for the company. If you were an oil engineer, would you want to work in the Niger Delta where you might be killed or kidnapped? So then they have to offer higher wages, more security, more bribes to the local police and army, and so on.
And this increased production cost gets passed on to others...