Mr al Mabhouh was found dead in his room at the Al Bustan Rotana in Al Garhoud on January 20, less than a day after arriving in the UAE.

Lt Gen Dahi Khalfan Tamim, the Dubai police chief, told a press conference tonight that six of the suspects came from the United Kingdom, three - including one woman - were from Ireland and one each were from Germany and France. He had previously said the death displayed the mark of Mossad, the Israeli security agency.

Two Palestinian nationals, both UAE residents, are also in Dubai Police's custody.

The 11 suspects stayed in various hotels across the city to distract police, Gen Tamim said. Footage of the men moving around the hotel was shown to reporters, who were also told that none of the suspects used phones while in the country and instead communicated by coded message.

Mr al Mabhouh had been tracked by the group since his arrival in the UAE, Gen Tamim said, and one of the group posed as a hotel employee to alert others should anyone threaten to interrupt the murder taking place.

Gen Tamim had previously said no bodyguards accompanied him on the trip, adding that the method used to kill him was a “Mossad method”, referring to the Israeli foreign intelligence service.

He added that Mossad “has carried out operations” in the past using similar procedures. He also said earlier this month that at least seven suspects, all holding passports from Western European countries, had been identified.

The exact methods used in Mr al Mabhouh’s killing have not been revealed. However, initial forensic reports suggested that he was given an electric shock before being suffocated. Further tests are being conducted. Police suspect other factors could have contributed to his death, including poisoning.

Since the beginning of the investigation, authorities have declined to rule out Mossad’s involvement in the killing.

Mr al Mabhouh arrived in the UAE on January 19 about 3.15pm and was dead within five hours, police have said. His assailants had been in the country less than 24 hours before the killing and left before his body was discovered in his hotel, they said.

Mr al Mabhouh, 50, was a founder of Hamas’s military wing, the Ezzedeen al Qassam Brigades. He was wanted by the Israeli government in connection with the kidnappings of two Israeli soldiers in 1989. Hamas has accused Mossad of carrying out the assassination. The Israeli government has declined to comment on the claims.