They identified the passports the 11 suspects were using as coming from Britain, France, Germany and Ireland

Dhahi Khalfan, Dubai's police chief, on Saturday said further investigation showed that some of those passports - bearing authentic holograms - had been used to track al-Mabhouh on earlier trips to the emirate.

'Security breach'

Al-Mabhouh took off from Damascus, the Syrian capital, on a flight bound for Dubai on January 19. Israel apparently suspected he was on his way to Iran to arrange an arms shipment for Gaza.

Around five hours after he checked in to the Al Bustan Rotana Hotel, he was murdered.

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Hamas officials are now saying al-Mabhouh may have inadvertently made some security slip-ups by booking his flight online, and by calling his family.

"Al-Mabhouh called his family by phone before he travelled to Dubai and told them of his plan to stay in a specific hotel, and he booked his travel through the internet," Salah Bardawil, a Hamas politician in Gaza, told reporters on Friday.

"This undoubtedly created a security breach in the movements of al-Mabhouh."

Bardawil also said some members of rival Palestinian faction Fatah may have had a role to play in the Hamas commander's death, but made no accusations against the group itself.

"We hold the Mossad directly responsible for the assassination of Mahmoud al-Mabhouh on Arab territory and the Mossad should, and will, bear all the consequences for this crime sooner or later," he said.

"We are not blaming Fatah or the Palestinian Authority. Until now, the investigations only point to collaborators or individuals who worked with Mossad. But this does not mean the PA of Fatah were behind the assassination."

The Israeli government, and Mossad itself, have refused either to confirm or deny any role in the assassination - part a "policy of ambiguity", as Avigdor Lieberman, the Israeli foreign minister, described it.

"Ultimately people here are quite satisifed by the outcome, whether it was in fact the Mossad or not, whether the faces of the operatives were shown on the CCTV cameras, whether or not there is a certain amount of diplomatic embarrassment," Al Jazeera's Jacky Rowland, reporting from Tel Aviv, said.

"That this Hamas senior commander, who was believed to be involved in gaining finance for weapons for Hamas fighters, the fact that he was taken out is something that most Israelis would approve whole heartedly of.

"There is nothing politically controversial here ... the question more is the rather messy loose ends that have been left here."

Diplomatic tensions

Tensions between Israel and its European allies have, however, mounted in the wake ofthe murder, with UK, Irish, German and French governments all summoning their respective Israeli ambassadors for answers regarding the use of their passports.

On Saturday, Germany's Der Spiegel magazine reported that the German passport used was genuine(in German).

The magazine said a man using the name of Michael Bodenheimer approached Cologne immigration officials in June 2008 with a request for citizenship, offering pre-World War II papers as proof of his German ancestry. The travel document was apparently issued in 2009.

The passport was apparently obtained by stealing the identity ofan Israeli-American.

UK authorities, meanwhile, said on Saturday that they believe the six British passports used in the operation must have been duplicates using numbers copied by Israeli immigration officials, according to a Telegraph report.  

The British travel documents were not biometric, meaning they did not have computer chips embedded in them that would make it more difficult to duplicate.