LAGOS, Nigeria - Admitting Islamic extremists now control some of his nation's villages and towns, Nigeria's president declared a state of emergency Tuesday across the country's northeast, promising to send more troops to fight what he said was an open rebellion.

President Goodluck Jonathan, speaking live on state radio and television networks, also warned that any building suspected of housing Islamic extremists would be taken over in what he described as the war now facing Africa's most populous nation. However, it is unclear what the emergency powers will do to halt the violence, as a similar past effort failed to stop the bloodshed.

"It would appear that there is a systematic effort by insurgents and terrorists to destabilize the Nigerian state and test our collective resolve," Jonathan said.

The president said the order would be in force in Adamawa, Borno, and Yobe states. He said the states would receive more troops, though he will not remove state politicians from their posts. Under Nigerian law, the president has the power to remove politicians and install a caretaker government in emergency circumstances.

The speech offered the starkest vision of the ongoing violence, often downplayed by security forces and government officials. Jonathan described the attacks as a "rebellion," at one point describing how fighters had destroyed government buildings and "taken women and children as hostages."

Since 2010, more than 1,600 people have been killed in attacks by Islamic insurgents, according to an Associated Press count. Recently, Nigeria's military has said Islamic fighters now use antiaircraft guns mounted on trucks to fight the nation's soldiers, likely outgunning the country's already overstretched security forces.

It remains unclear how much effect Jonathan's announcement will have. In late 2011, he declared a similar state of emergency over parts of four states, including Borno and Yobe. The extremist attacks continued.

Nigeria's military and police also have been repeatedly accused by human-rights activists and others of torturing and summarily killing suspects.