The main militant group in Nigeria's oil-rich southern region, has vowed massive retaliation for Saturday's offensive on its positions by the army.  Gilbert da Costa has more in this report from Abuja.

The Movement for the Emancipation of the Niger Delta, is warning oil companies to pull workers out in the next 24 hours or face what it called "a hurricane of retaliation".  

Analysts say attacks in the Niger Delta have become more frequent and intense because government forces are losing control in the area.

Nigerian President Umaru YarAdua (File photo)

Nigerian President Umaru Yar'Adua has come under pressure to quell the unrest.  The weekend 's army offensive could herald the government's adoption of a more muscular approach towards militancy in the Niger Delta.

But the militants say they are not afraid to take on the military.  A rebel commander, Tom Polo, who spoke to VOA in Pidgin English, says rebels plan to increase attacks before  Nigeria's Independence Day on October 1.  The militants have sufficient men, weapons and ammunition, he says, to counter the Nigerian military.

Nearly two decades of unrest in the Niger Delta have in recent years evolved into an armed insurgency for local control of the region's oil wealth.

Militants say the Delta does not get a fair enough share of the huge revenues it makes for the country.

The government attempt to negotiate a settlement with the rebels collapsed in August.

The rebels increasingly bold campaign in the region has slashed Nigeria's crude oil output by more than 20 percent.

Nearly 300 foreigners have been seized in the Niger Delta since early 2006.  Almost all have been released unharmed.  A group of 27 oil workers kidnapped last week is still being held.