The declaration gives President Olusegun Obasanjo sweeping powers and he immediately exercised them by replacing the elected governor with a former military general and dissolving the state legislature.
In an address on state radio, Obasanjo said Gov. Joshua Dariye and other elected state officials had ``wittingly and unwittingly encouraged acts that have subverted peace and tranquility.''
Replacing Dariye is retired Maj. Gen. Chris Ali, a state resident who served in the Nigerian army under previous junta rulers.
``We need to take serious steps to stem the tide of what has become a near-mutual genocide in the affected areas of Plateau state,'' Obasanjo said. ``In my personal and official capacities, I have done everything to bring lasting peace to Plateau state.''
The fighting in Plateau began in September 2001 in the previously tranquil city of Jos. More than 1,000 were killed. The bloodletting escalated earlier this month with the killings of hundreds of Muslims by members of a Christian ethnic militia in the town of Yelwa.
Muslims rioted last week in the northern city of Kano, attacking Christians and killing scores in apparent revenge for the Yelwa killings.
Christian and Muslim groups have both accused Dariye of siding against them in the violence.
Dariye's spokesman, Stanley Bentu, said the governor accepted Obasanjo's declaration, but declined further comment.
Obasanjo, 66, is a former military general who in 1979 became Nigeria's first junta leader to voluntarily step aside. He returned to politics two decades later as an elected civilian. He was re-elected last year in a vote rejected as rigged by his main opponent, former military ruler Muhammadu Buhari.
© 2004 AP