Nigerian President Goodluck Jonathan declared a state of emergency on Tuesday across the troubled northeast, after a deadly offensive by Islamist militant groups.

The president also ordered more troops to be deployed in the three north-eastern states of Adamawa, Borno and Yobe where a state of emergency has been imposed, and warned that any building suspected of housing militants would be taken over, the Associated Press reported.

“It would appear that there is a systematic effort by insurgents and terrorists to destabilize the Nigerian state,” Jonathan said in a pre-recorded address broadcast on Tuesday.

According to Nigerian law, the president can install a caretaker government in emergencies, but Jonathan said he would not remove state politicians from their posts, the AP reported.

Thousands of people have died in Nigeria over the past few years in communal strife fueled by Boko Haram, a militant Islamist group with reported ties to al-Qaida. The imposition of  Islamic law in several northern states by Islamists has caused thousands to leave the region.

Separatist aspirations have also been on the rise in Africa’s most populous nation,  a reminder of the Biafran conflict in the late-1960s, during which more than one million people died, mostly from poverty and disease.

“Already, some northern parts of Borno state have been taken over by groups whose allegiance are to different flags than Nigeria’s,” Jonathan said. “These actions amount to a declaration of war and a deliberate attempt to undermine the authority of the Nigerian state,” he said.

“What we are facing is not just militancy or criminality, but a rebellion and insurgency by terrorist groups which pose a very serious threat to national unity and territorial integrity,” he said.

A former British colony, Nigeria is one of the world’s largest oil producers but is affected by a spate of conflicts over land, religion and oil.

Doyin Okupi, a spokesman for the president, told the BBC that the governors of Borno, Yobe and Adamawa had been “very well briefed” and were “in full support” of the decision to declare a state of emergency.

“There's a need for the government to step in and do the necessary to once and for all find a way out of this quagmire,” he said.

In the latest violence, 53 people were killed and 13 villages burnt in central Nigeria's Benue state on Tuesday.