Police have targeted 17 people in raids in several European countries connected to a suspected “jihadist network”.
Six suspects were detained in Italy, four in Britain, and three in Norway. Police believe some of the suspects may have travelled to Syria or Iraq.
Italy’s Ansa news agency said the suspects were accused of international terrorism association.
The network was allegedly plotting to free its leader, Mullah Krekar, who is already in prison in Norway.
Krekar, born Najm Faraj Ahmad, and two others were arrested in Norway as part of the operation, on suspicion of plotting attacks in Norway and other European countries, according to Italian police.
They face extradition to Italy.
Krekar, the Iraqi Kurdish founder of the radical Islamic group, Ansar al-Islam, has served several jail sentences in recent years, including for praising the killing of staff at the French satirical newspaper Charlie Hebdo.