Militants from Nigeria's oil-rich Delta have called off a voluntary ceasefire, promising a fresh campaign of violence and kidnappings of oil workers.
Mend want more oil revenues to benefit local communities
In a statement e-mailed to reporters on Sunday, the Movement for the Emancipation of the Niger Delta said attacks would recommence from midnight.
Mend announced a voluntary truce after the May inauguration of President Umaru Yar'Adua, but says talks have failed.
Previous attacks on oil installations have slashed ouput of Nigerian crude.
Mend's main demand is for the Delta region to control its oil resources and pay tax to the federal government, but the line between ideological struggle and crime is blurred.
The Mend statement said: " There will be no forewarning of these attacks but a statement will follow soon after."
Formed early 2006
Close links to militant Mujahid Dokubo-Asari's Niger Delta Volunteer Force
Split into two rival groups late 2006
Bayelsa State faction leader - Jomo Gbomo
Delta State faction leader - Gen Godswill Tamuno
Demand 100% control of Nigeria's oil wealth
Demand release from jail of Dokubo-Asari being tried for treason
Demand release of impeached Bayelsa governor on trial for money laundering
Operate from creeks of Niger Delta
Communicate with media by e-mail
The group said its decision was a response to the arrest of one its leaders, Henry Okah, in Angola, which they claim was orchestrated by the Nigerian authorities.
Both Nigeria and Angola have so far declined to comment.
According to his Johannesburg-based wife, Mend faction leader Henry Okah, who in the past is believed to have used the alias Jomo Gbomo, had gone to Angola to buy a ship and was boarding a plane to return to Johannesburg when he was detained on 3 September.
Security sources believe Okah and Gbomo are the same person.
Azuka Okah told the Reuters news agency: "Two days later I got a call to say he was in custody on arms trafficking and money-laundering charges."
The Niger Delta is home to all of Nigeria's oil, responsible for 95% of hard currency earnings, but most of the peoples of the Delta live in abject poverty.
Corrupt officials siphon off millions of dollars destined for basic services and development, and many are also accused of involvement in the trade in crude oil stolen from pipelines crossing the region, civil society groups say.
Rivers State officials - including the deputy governor - have been accused of being secretly in control of the gangs.
Last week, President Yar'Adua ordered an investigation into alleged links between government officials in the Niger Delta and violent criminal gangs.