The United States consulate in Lagos warned on Friday that a militant group in Nigeria's oil producing Niger Delta may have imminent plans to launch a campaign of bombings, attacks on oil facilities and hostage takings.
The warning comes a day after armed attackers kidnapped an American and a Briton from a ship off the coast of Bayelsa state in the delta, the latest in a wave of attacks on the oil industry in the world's eighth largest exporter.
The attacks have forced hundreds of workers to pull out and cut oil output by 500,000 barrels a day since February.
Dramatic threats by Niger Delta groups are common and are not always carried out.
The US consulate said on October 4 that militants may target Bonny Island, a major oil and gas export hub but no attack has materialised.
"The US government has learned that as of late October 2006, a militant Niger Delta group may have finalised its plans for a unified attack against oil facilities in the Niger Delta region," the consulate said in a circular.
"The attacks allegedly will be carried out sometime during the first week of November and will include 10 to 20 simultaneous bombings of land-based targets and a series of separate attacks on oil installations in which expatriate workers will be taken hostage," it said.
The circular said no details were available as to the specific targets of the planned attacks.
The consulate was elaborating on an earlier warning published on Thursday, in which it alerted US citizens to the risk of further attacks and hostage takings in the delta.
Several recent abductions have been motivated by ransom, although militants demanding more regional autonomy are also a growing force.
Disputes between oil companies and communities over jobs and other benefits often also play a role.
Hostages are rarely harmed in Nigeria, and are usually released after money changes hands.
Violence in the delta is rooted in poverty, corruption and lawlessness. Many residents of the impoverished region resent the multibillion-dollar industry for damaging their environment while bringing them few benefits.
Turf wars over control of a lucrative trade in stolen crude, abductions for ransom and sabotage fomented for political ends all add to the momentum of violence.
Many in the delta fear the situation could deteriorate further in the run-up to general elections in April.