Exiled Chechen rebel leader Akhmed Zakayev has been detained for questioning in Poland where he is attending a congress.
Viewed by Russia as a terrorist, he was granted political asylum by Britain in 2003.
He travelled to Poland to attend a two-day Chechen conference despite authorities there warning him they would have no choice but to arrest him. Moscow has issued an international warrant against him through Interpol.
Zakayev fought Russia as a senior rebel commander in two wars in the 1990s. Today, he represents the moderate wing of the separatist Chechen movement.