The U.S. State Department has designated Somalia's al-Shabab insurgent group as a foreign terrorist organization.

The announcement was officially published Tuesday in the U.S. federal register.

The announcement says the group has committed or poses a risk of committing acts of terrorism that threaten the security of U.S. nationals, or the national security, foreign policy or economy of the United States.

In recent months the Islamist militant group has claimed responsibility for a series of bombings and attacks on Somali government and Ethiopian soldiers.

Last week, members of al-Shabab beheaded three government soldiers during an ambush on a checkpoint outside the capital, Mogadishu. In February, the group claimed responsibility for bombings that killed 20 people, mostly Ethiopian migrants.

The insurgency began after a joint Somali-Ethiopian offensive drove Islamists from power in Mogadishu and other Somali cities in late 2006.

Fighting has killed thousands of people in Mogadishu alone and forced at least a half million others to flee the city.

Somalia has not had a stable central government since 1991.