The U.S. has designated Nigeria’s Boko Haram and Ansaru militant groups as foreign terrorist organisations.

The state department described the move as “an important” step to help Nigeria “root out violent extremism”.

“These designations are an important and appropriate step, but only one tool in what must be a comprehensive approach by the Nigerian government to counter these groups,” a State Department statement said.

This means that the U.S. justice system is now empowered to block all financial dealings or transactions between America and these organisations.

The groups have been responsible for thousands of deaths in northeast and central Nigeria, including attacks on churches and mosques and a 2011 suicide bombing of the United Nations building in Abuja, the statement said.

“By cutting these terrorist organizations off from U.S. financial institutions and enabling banks to freeze assets held in the United States, these designations demonstrate our strong support for Nigeria’s fight against terrorism and its efforts to address security challenges in the north,” Lisa Monaco, President Barack Obama’s top homeland security and counter terrorism adviser, said in the statement.

“We encourage Nigeria to pursue a comprehensive counter terrorism approach that uses law enforcement tools effectively, creates economic opportunity and ensures that human rights are protected and respected,” she said.