Passports belonging to the alleged killers of a top Hamas official in Dubai are fraudulent, the British and Irish governments have said.
Ireland said the names and passport numbers of three suspects did not match anything issued by its officials.
Britain said it believed the six British passports were also fraudulent.
Arrest warrants were issued for the suspects named by police in Dubai, where Mahmoud al-Mabhouh was murdered in a hotel room on 20 January.
Two more men, one using a French passport and one using a German passport, are also suspected of playing parts in the assassination.
The French foreign ministry said it was “not able to confirm the nationality of this person”, according to AFP news
German officials said the passport number was either incomplete or wrong, Associated Press reported.
Reports have suggested that Mr Mabhouh was in Dubai to buy weapons for Palestinian Islamist movement Hamas.
I don’t know how this happened or who chose my name or why, but hopefully we’ll find out soon
Melvyn Adam Mildiner
Hamas have accused Israeli agents of killing him.
A day after Dubai police announced the names of the Irish suspects as Gail Folliard, Evan Dennings and Kevin Daveron, a spokesman for Ireland’s Department of Foreign Affairs said: “We are unable to identify any of those three individuals as being genuine Irish citizens.
“Ireland has issued no passports in those names.”
The passport numbers had the wrong number of digits and did not contain letters as authentic passports do, he added.
“These purported passports are false. These are not genuine passports.”
Gordon Corera, BBC News, security correspondent
Taking on a different identity is a regular occurrence for intelligence agents on undercover missions. Spies often have a stack of passports under different names ready to go.
It is more difficult and potentially more sensitive to take on a different nationality – and particularly if you are found out, since it can lead to diplomatic protests.
One way of falsifying a nationality is to forge a passport or insert a new identity and picture into a stolen passport.
But a more effective way can be to steal a real person’s identity and get a real passport in their name.
There are suspicions that Israel’s Mossad was involved, particularly since it has used foreign passports for previous operations including the 1997 attempt on the life of Khaled Meshal in Jordan, when two operatives used Canadian passports.