Nairobi/Abuja - Nigeria's main militant group Wednesday threatened to unleash anarchy in the oil-rich Niger Delta should government officials accused of siphoning off funds in one of the region's states not be dealt with harshly.

Nigeria's Economic and Financial Crimes Commission (EFCC) said Tuesday it had arrested the chief of staff to the governor of Rivers state and the secretary of the state government as it probes irregular withdrawals of large sums from government accounts.

"If we are not satisfied with the measure of justice meted out, we will make Rivers State ungovernable by creating a state of anarchy," Jomo Gbomo, spokesman for the Movement for the Emancipation of the Niger Delta (MEND) said in a statement.

MEND attacked platforms, pipelines and oil flow-stations owned by Chevron, Shell and Agip during a six-day "oil war" in mid-September and claimed to have killed dozens of soldiers.

Shell said it may not be able to meet contractual obligations due to the violence.

Militant groups such as MEND often attack oil installations and kidnap expatriate workers, saying they are fighting for a greater share of profits from oil exploitation for the poor of the region.

The government says they are merely criminal gangs intent on stealing oil and extorting money.

The unrest has cut oil production by around a fifth since early 2006, helping to push up global oil prices and allowing Angola to surpass Nigeria as Africa's biggest oil exporter.

The Niger Delta is one of Nigeria's biggest concerns, and President Umaru Yar'Adua recently set up a new ministry to develop the region last month.

It has received a lukewarm response, however.

An earlier government body designed to improve the region proved ineffectual and was hit by a major corruption scandal. (dpa)