The main militant group in Nigeria's restive Niger Delta region has declared all out war In the area.
In an e-mail to the media Friday, the rebel group Movement for Emancipation of the Niger Delta (MEND) claimed the Nigerian armed forces had launched what it called indiscriminate aerial attacks on civilians in the region, killing mostly women, children and the elderly.
Residents in the region confirmed fighting had taken place.
The group called on all men "of fighting age" to join their cause. MEND also restated its call for oil companies to evacuate their personnel by midnight Friday to avoid being caught in the conflict.
A Nigerian military spokesman told reporters the army had been carrying out what he called "cordon and search" operations in the region since the militants seized two ships in the region Thursday. He gave no details on the army's operations.
The militants hijacked the oil tanker MV Spirit on Wednesday and continue to hold the ship's 15-member crew hostage. They also seized a cargo ship. Local media have reported that at least 20 foreigners are among the crew abducted in the two attacks.
The rebels claimed Nigerian armed forces had launched an attack on two MEND camps early Wednesday. They also claimed they have attacked Nigerian military bases in retaliation.
A Nigerian military spokesman confirmed that the Wednesday morning battle had occurred but said that it was provoked by MEND.
Kidnapping and violence is common in the Niger Delta. Militants say they are fighting for a larger share of oil wealth for local inhabitants, but the government calls them "criminals."
Some information for this report was provided by AFP and Reuters.