ABUJA, Nigeria — Nigeria’s military on Friday named the Indigenous People of Biafra a terrorist organization, targeting a movement that 50 years ago tried to create a state for the Igbo people.

The declaration comes amid rising calls for secession in the southeast and reports of recent clashes between supporters and security forces. The movement’s leader, Nnamdi Kanu, was freed earlier this year following a 2015 arrest that led to protests. He had been accused of terrorism.

The Nigeria’s military statement claimed the Indigenous People of Biafra has formed a secret service and national guard, and it dismissed the movement’s claims that its actions are nonviolent. The movement could not immediately be reached for comment.

Africa’s most populous nation already faces the deadly threat of Boko Haram extremists in the country’s northeast and militants in the oil-rich Niger Delta.

President Muhammadu Buhari last month in a televised address vowed to “reinforce and reinvigorate the fight” not only against Boko Haram but against “ethnic violence fueled by political mischief makers.”

Buhari, a former military dictator in the 1980s, was a brigade major who commanded troops in Biafra during the civil war decades ago in which soldiers were accused of mass atrocities.

Members of the separatist movement in May marked 50 years after that civil war saw more than one million people die, many of starvation, trying to create a state for the Igbo people. The Igbo are one of Nigeria’s largest ethnic groups but remain largely marginalized in politics.

A Biafran state would include Nigeria’s richest and devastatingly polluted oil-producing areas, already riven by violent demands for a more equitable share of wealth from one of Africa’s biggest petroleum producers.

Amnesty International Nigeria said in a statement Friday it was “deeply concerned by reports of violence across Nigeria following clashes between the military and supporters of IPOB.” The rights group called on security forces to avoid using excessive force.