The United States has named Nigerian-based militant groups Boko Haram and Ansaru as foreign terrorist organizations.
In a statement Wednesday, U.S. counterterrorism official Lisa Monaco said the two groups have been responsible for thousands of deaths in northeast and central Nigeria in recent years.
She said the groups have carried out dozens of attacks on churches and mosques, as well as targeted killings of civilians. U.S. officials blame Boko Haram for a 2011 attack on a U.N. building in Abuja that killed 21 people.
The designation cuts off Boko Haram and Ansaru from U.S. financial institutions and allows banks to freeze their assets held in the United States.
The announcement came as a U.S. Congressional subcommittee holds a hearing on the threat posed by Boko Haram, Nigeria's most prominent militant organization.
Earlier this year, Ansaru declared itself a splinter group independent of Boko Haram. U.S. officials said Ansaru's attacks have focused mostly on Nigerian military and Western targets.
Before Wednesday's hearing, committee chairman Christopher Smith said Boko Haram fit the definition of a terrorist group and should be designated as such.
Boko Haram's name in the Hausa language means "Western education is a sin." The group has battled the Nigerian government since 2009, with frequent attacks on police stations, jails, and government officials, as well as civilian targets like churches and mosques.
The group is believed to be fighting for an Islamic state in northern Nigeria, although much about its membership, leadership and structure remains unclear.
Last year, the U.S. State Department designated Boko Haram's most visible leader, Abubakar Shekau, a terrorist, along with two other men ( Abubakar Adam Kambar and Khalid al-Barnawi) who allegedly have ties to Boko Haram and al-Qaida in the Islamic Maghreb.
Nigeria's government declared a state of emergency in three northeastern states in May and has sent thousands of troops to battle the group. But attacks continue, amid accusations the military has killed hundreds of civilians through indiscriminate and heavy-handed violence.
The State Department said Wednesday that the designations were "only one tool" in what must be a comprehensive approach by Nigeria's government to counter the groups through law enforcement, political and development efforts, as well as military engagement.