A Yemeni secessionist leader was detained on Wednesday when his plane from Britain landed at Aden airport, a fellow leader of the separatist movement told Reuters.

“A group of armed men boarded the plane when it landed and arrested Ahmed Abdullah Al Hassani,” said Hussein Zayd bin Yahia, who was waiting for Hassani at the airport.

“They took him and disappeared. They were in three cars.”

The identity of the armed men was unclear but Yahia suggested they belonged to Yemeni security services. There was no immediate comment from Yemen government officials.

North and south Yemen formally united in 1990 but then fought a civil war in the early 1990s. Some in the south, home to many of Yemen’s oil facilities, say northerners have seized resources and discriminated against them.

Last year’s popular protests, which eventually led to the ousting of former President Ali Abdullah Saleh, increased secessionist sentiment in the south. Yemeni media reported earlier this week that Hassani, who had been living abroad, planned to visit Aden to meet with other secessionist leaders.

Besides the secessionist movement, which seeks to revive a southern socialist state, Yemen is grappling with problems including a violent insurgency by militants linked to Al Qaeda in the south and rebels in the 
north.