Amnesty International says two human rights activists in Indonesia's Aceh province are believed to be being held by the military and could face torture or death.

The British-based rights group says Mukhlis Ishak, 27, and Zulfikar, 24, were detained on March 25 by plain-clothed men believed to be from the military intelligence unit, Satuan Gabungan Intelijen.

The two members of a non-government organisation, Link for Community Development, were held while accompanying villagers staging a protest against plans to establish a Brimob paramilitary police post in their village.

An Amnesty statement says it is feared the pair were targeted by authorities for their human rights activism.

The rights group says security forces battling separatist rebels in Aceh had carried out grave human rights violations, including unlawful killings.

Amnesty has urged members and others to write to military and police officials expressing their concern for the activists.