Jihadist groups around the world
How many people have gone to Syria to fight?
British police confirmed that counter-terrorism units had arrested three men in their 30s and a 52-year-old from four locations in the Midlands and northern England.
Norway's Justice Minister Anders Anudsen said Italy had requested Krekar's extradition, but that it would need assurances that he would not be sent to Iraq.
The 59 year old, whose real name is NajmuddinFaraj Ahmad, has lived in Norway since 1991. The authorities have wanted to expel him since 2003, but are prevented from deporting him to Iraq, where he could face the death penalty.
Krekar's lawyer, BrynjarMeling, told the BBC that he had spent several hours with his client going through the accusations. He said that as far as he could tell the only charge against him was that he was the leader of RawtiShax.