Four men are due in court to face extradition proceedings after being arrested in Britain as part of an international investigation into an alleged Islamist terror network.
The suspects were among 13 arrested across Europe by investigators probing a group called Rawti Shax, which is described as a "terrorist organisation of Kurdish-Sunni origin".
The four men arrested in the UK on Thursday, who are not believed to be British nationals, are aged 38, 32, 33 and 52, from Hull, Derby, Birmingham and Sheffield respectively and will appear at Westminster Magistrates' Court today.
Suspects were also arrested in Italy and Norway, while authorities in Italy, Germany, Finland, Norway, Switzerland and the UK also searched a total of 26 properties and seized several items including electronic devices and documents.
Eurojust, the EU agency which co-ordinated the raids, said suspected leaders and several members of the group were arrested during simultaneous activity in six countries.
It added: "The arrested persons are charged with international terrorism."
The suspects were feared to be planning to target British diplomats following the imprisonment of the ideological leader of Rawti Shax, the Sun reported.
Najmuddin Faraj Ahmad, known as Mullah Krekar, was sentenced to 18 months in Norway last month for praising the killing of cartoonists at the French satirical newspaper Charlie Hebdo in January.
His lawyer told reporters in Norway that suspicions against him "have largely been based on false accusations".
Some suspects could not be located as they are believed to have travelled to Syria and Iraq to join jihadist organisations such as Islamic State (IS) - also known as Isis - and al-Nusra.
Rawti Shax or Didi Nwe - meaning the "new course" or "towards the mountain" - is said to represent an "evolution" of Ansar Al Islam, which is listed by the UN as a terrorist organisation affiliated with al Qaida.
Eurojust said: "Its primary objective is to violently overthrow the current Iraqi Kurdish government and replace it with a caliphate governed by Sharia law.
"According to the Italian investigation, unlike Ansar Al Islam, Rawti Shax arose and is rooted in Europe, with cells communicating and operating via the internet, with a structure active especially in Germany, Switzerland, the UK, Finland, Italy, Greece, Sweden, Norway, Iraq, Iran and Syria.
"As the group evolved, it became active in providing logistical and financial support to recruiting foreign terrorist fighters to be sent to Syria and Iraq, also with the intent of training them for the future conflict in Kurdistan."
Ansar Al Islam has been listed as a proscribed terrorist organisation in the UK since October 2005.
The operation, which follows several years of work by investigators, was launched under the direction of the Public Prosecution Office in Rome.
A spokeswoman for the North East counter-terrorism unit, who were involved with the arrests alongside West Midlands CTU, said they wanted to reassure people there is "no evidence to suggest that communities are at risk".