Police in Armenia have detained and raided the offices and homes of four opposition activists suspected of plotting riots on the centennial of the massacre of 1.5 million Armenians that Armenia describes as genocide.

The Investigative Committee said in a statement on Tuesday that four activists of the Founding Parliament opposition group, including its leader, are in custody. The group, however, says five of its members were detained.

Founding Parliament is a nationalist organization run by Jirair Sefilian, a battalion commander during a war over the ethnic Armenian enclave in Azerbaijan.

Sefilian's group was planning anti-government protests on April 24 in Armenia's capital Yerevan to commemorate 100 years since the massacre of Armenians by Ottoman Turks. The killings are widely viewed by scholars as the 20th century's first genocide.