The 13 suspected members of a jihadist group arrested in raids across Europe were allegedly recruiting foreign fighters to be sent to Iraq and Syria.
The raids in Finland, Germany, Italy, Norway, Switzerland and the UK targeted Rawti Shax, which seeks to establish a caliphate in Iraq's Kurdistan region.
Among those arrested was the group's imprisoned leader, Mullah Krekar.
Italian police said the group was also planning attacks with the aim of securing his release by Norway.
Krekar, an Iraqi Kurd, is serving an 18-month sentence for making threats and encouraging others to commit criminal acts.
Thursday's raids saw suspected leaders and members of Rawti Shax arrested in Italy, Norway and the UK, and premises searched in Germany, Finland and Switzerland.
Gen Giuseppe Governale of the Italian Carabinieri's Special Operations Group, which launched the investigation, told journalists in Rome that the operation constituted "the most important police operation in Europe in the last 20 years".
It had "dismantled an integrated cell" that had developed "on the 'dark web', little-known [internet] platforms that we have managed to penetrate", he said.
The cell, the general alleged, "was about to continue sending many other jihadists abroad; it was about to carry out attacks, including suicide bombings, to try to free their chief, Mullah Krekar".
The attacks could have targeted Norwegian and British diplomats, Italian media cited Gen Governale as saying.
However, the European Union's Judicial Co-operation Unit (Eurojust), British police, and the Norwegian Police Security Service could not confirm the existence of a plot against diplomats.
- Came to Norway as a refugee in 1991 from Iraq
- Founded Ansar al-Islam, although he later tried to distance himself from the radical Islamist group
- Norwegian authorities have been trying to deport him since 2003 after deeming him a threat to national security. However, under Norwegian law, he cannot be deported to Iraq because he could face the death penalty
- Jailed in 2012 for making death threats against officials and others
- Detained again in February 2015 after praising the Charlie Hebdo attack during a television interview
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 Najmuddin Faraj 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, Brynjar Meling, 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 Rawti Shax.
Mr Meling denied Rawti Shax was a terror organisation, describing it as a platform for sharing ideas with political aspirations for the future.
Eurojust said Rawti Shax, or Didi Nwe, (the "new course" or "towards the mountain") represented an "evolution of Ansar al-Islam", which is listed by the UN as a terrorist organisation affiliated with al-Qaeda.
It alleged that the group was active in providing logistical and financial support for the recruitment of foreign fighters to be sent to Syria and Iraq - where jihadists from Islamic State (IS) and an affiliate of al-Qaeda control large swathes of territory - and also had the intent of training them for the future conflict in Kurdistan.