At the same time Interpol issued arrest notices for 11 suspects -- six listed with British passports, three Irish, one French and one German -- wanted by Dubai for the killing of Hamas commander Mahmud al-Mabhuh in the emirate.
Amid mounting diplomatic tension, British Foreign Secretary David Miliband urged the Israelis to cooperate "fully" in investigating the incident.
"We want to get to the bottom of the issue of the fraudulent passports, or their potential use," Miliband said after Israeli ambassador Ron Prosor held talks with Peter Ricketts, the head of Britain's diplomatic service.
In Dublin, Irish Foreign Minister Micheal Martin announced "frank" talks with Israel's envoy -- usually diplomatic code for angry exchanges -- saying he regarded the use of false passports as "an extremely serious incident".
"Regardless of who was responsible, (Ireland) takes grave exception to the forgery and misuse of Irish passports which could devalue the standing of the passports and potentially put at risk the safety of Irish citizens," it said.
The country's foreign ministry meanwhile revealed it believed five fake Irish passports, rather than three, were linked to the hit.
New information provided from Dubai authorities linked two other forged Irish passports to the killing, said the ministry.
A spokesman said that Ireland had heard reports that, in addition to the 11 names already identified, there may be up to eight others involved.
The ministry believes the two additional Irish fake passports could have been used by two of these eight.
In Paris, a spokesman said the foreign ministry had "expressed France's deep concern about the malicious and fraudulent use" of a French passport in a meeting with Israeli charge d'affaires Sammy Ravel.
Germany meanwhile demanded an explanation from Israel over the killing, in a meeting between a top foreign ministry diplomat and the Israeli charge d'affaires in Berlin.
"In view of the information revealed so far I believe it is imperative to clear up thoroughly the circumstances surrounding Mahmud al-Mabhuh's death," Foreign Minister Guido Westerwelle said in a statement.
Diplomatic tensions have mounted over Mabhuh's killing after Dubai's police chief revealed that 11 European passport holders were allegedly involved.
No government has directly accused Israel but speculation about the killers has centred on Israel's Mossad intelligence services, which have used agents with fake passports for such operations in the past.
Dubai police chief Lieutenant General Dahi Khalfan Tamim said he was near certain Mossad was to blame and wanted its the agency's head, Meir Dagan, to bear responsibility.
"If the Mossad were proven to be behind the crime, which is most likely now, Interpol should issue a Red Notice for the head of the Mossad because he would be a killer," Lieutenant General Dahi Khalfan told Dubai TV.
And the use of fake passports of countries with normally friendly ties with Israel is generating anger in London, Dublin, Paris and Berlin.
British Prime Minister Gordon Brown -- whose country's ties with Israel were already chilled by a recent row over an arrest warrant issued for ex-foreign minister Tzipi Livni -- stressed Thursday the need for a "full investigation."
Britain's Serious Organised Crime Agency will lead the probe in cooperation with the United Arab Emirates authorities, a government spokesman said.
Announcing the issue of the so-called Red Notices, Interpol said it "has reason to believe that the suspects linked to this murder have stolen the identities of real people."
------------------------------------------------------------------------