In a sharp escalation of diplomatic tensions between Britain and Israel, Israeli Ambassador to London Ron Prosor was on Thursday called to the Foreign Office to explain how fake passports of six Israeli-based British citizens came to be used by the killers of a Hamas commander, Mahmoud al-Mabhough, in a Dubai hotel last month.

The killing was suspected to have been carried out by a Mossad hit-squad though Israel has denied its involvement.

Mr. Prosor declined to comment as he emerged from a reportedly tense 20-minute meeting with permanent under-secretary to the Foreign Office Sir Peter Ricketts, but Foreign Secretary David Miliband said Israel had been told that Britain took the issue “very seriously'' and was determined to “get to the bottom'' of the incident.

He said Israel was also told to cooperate fully with the investigation ordered by Prime Minister Gordon Brown.

The investigation would be conducted by the Serious Organised Crime Agency (SOCA). “Sir Peter made clear to Mr. Prosor how seriously we take allegations of the fraudulent use of passports. We will give Israel every opportunity to share with us what they know. We hope and expect they will cooperate with the investigation by SOCA,” he said.

A similarly tough line came from Dublin as the Irish Government summoned Israeli Ambassador Zion Evrony to convey its concerns over the use of forged Irish passports.

As Britain hardened its position, media reports said it could consider scrapping its intelligence-sharing arrangement with Israel if it was proved that Mossad was involved in stealing the identities of British citizens.

“If the Israelis were responsible for the assassination in Dubai, they are seriously jeopardising the important intelligence-sharing arrangement that currently exists between Britain and Israel,'' The Daily Telegraph quoted a senior Foreign Office official as saying.

In the 1980s, the Government closed down Mossad's operation in Britain after it was found to have been involved in forging British passports and was allowed to resume work only after it promised that such things would not happen again.

Mr. Brown said British passport was an “important part of being British'' and Britain wanted to make sure that everything was done to protect it. “We have to carry out a full investigation into this. The evidence has to be assembled about what actually happened, about how it happened and why,'' he said amid calls for the Israeli ambassador to be sent back if he was not able to provide satisfactory explanation.

Britain is among the 11 European countries whose forged passports were used by Mahmoud's killers.

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