At least two people were killed in a clash between Nigerian state security officers and a group campaigning for the secession of a part of southeastern Nigeria formerly known as Biafra, security services said on Sunday.

The incident between the Department of State Services (DSS) agents and members of the outlawed Indigenous People of Biafra (IPOB) took place in southeastern Nigeria’s Enugu state.

According to DSS, two of its personnel were killed in what they called an unprovoked attack, while IPOB, in a statement, said 21 of their members were killed and more than 40 others arrested after security forces stormed one of their meetings.

DSS did not immediately respond to queries on IPOB member deaths. IPOB described itself as a peaceful group and denied killing any DSS agents.

IPOB leaders have called for secession in the region, where tensions have simmered since a Biafra separatist rebellion sparked a civil war in 1967-70 that killed an estimated one million people.

In 2017, Nigeria’s armed forces designated IPOB as a “terrorist organization” after it stepped up calls for secession.