Gordon Brown today promised a "full investigation" into the use of faked British passports by a hit squad who assassinated a Hamas commander in Dubai.
The Prime Minister said: "We are looking at this at this very moment."
"We have got to carry out a full investigation into this. The British passport is an important document that has got to be held with care," he told London's LBC Radio.
"The evidence has got to be assembled about what has actually happened and how it happened and why it happened and it is necessary for us to accumulate that evidence before we can make statements."
He spoke amid demands for the Israeli ambassador to be summoned to the Foreign Office to answer allegations that its security services were behind the assassination.
Two of those whose British passports were apparently used by the killers have expressed their shock at being named among 11 suspects identified by Dubai police.
While details such as the names, numbers and dates of birth on the suspect passports matched the originals, the photographs and signatures differed.
The Foreign Office has said the six British passports involved were "fraudulent" and officials in Dublin said they had "issued no passports" in the names of three people using Irish identities.
Hamas has pointed the finger at Israel, blaming Mossad - the country's secret service - for carrying out last month's hit on Mahmoud al-Mabhouh in Dubai.
And Dubai's police chief Lieutenant General Dhahi Khalfan Tamim said it was possible that "leaders of certain countries gave orders to their intelligence agents to kill" the Hamas man.
Israel's foreign minister said there was no reason to think that Mossad was behind the assassination but offered no explicit denial.
Avigdor Lieberman said Britain recognised Israel as a "responsible" country that held to "clear, cautious and responsible rules of the game".
But he told Army Radio in Israel that a "policy of ambiguity" on security matters meant he would not comment directly on the allegations.
"Israel never responds, never confirms and never denies. There is no reason for Israel to change this policy," he insisted.
But former Liberal Democrat leader Sir Menzies Campbell, who is also a member of the Commons Foreign Affairs Committee, said the Government should demand answers from the Israeli ambassador.
"If the Israeli government was party to behaviour of this kind it would be a serious violation of trust between nations. If legitimate British passport holders were put at risk it would be a disgrace," he said.
"Given the current speculation, the Israeli government has some explaining to do and the ambassador should be summoned to the Foreign Office to do so in double-quick time."
Tory MP Hugo Swire, chairman of the Conservative Middle East Council, had also called for a "full investigation".
The names on the faked UK documents were Michael Lawrence Barney, James Leonard Clarke, Jonathan Louis Graham, Paul John Keeley, Stephen Daniel Hodes and Melvyn Adam Mildiner.
Israel-based Mr Mildiner, 31, who holds a British and Israeli passport that matches one released by Dubai police, said he had never been to Dubai and said it was a "horrid" situation.
Although the name and number of the travel papers matched his own, the date of birth was off by a few days, he said.
Kent-born Paul Keeley, 42, a builder who has lived on a Kibbutz in northern Israel for the past 15 years, told the Daily Telegraph he had not left Israel for two years.
"When I first heard about this I immediately looked to make sure my passport was still there and it was," he said. "It has not been stolen so I don't know what on earth has happened.
"It is all very worrying but I know I have not done anything wrong."
Al-Mabhouh died in his luxury hotel room near Dubai international airport on January 20. It is claimed he was suffocated.
It is alleged that the hit squad flew into Dubai on separate planes and booked into different hotels wearing wigs and fake beards to disguise their appearances.
At least two of the alleged gang watched the Hamas commander check-in to the hotel and booked a nearby room, it was further claimed.
Around five hours after setting foot in the city-state, al-Mabhouh was ambushed and killed. It is not known if he opened the door to his alleged killers himself.
All of the suspects left the United Arab Emirates within 19 hours of their arrivals, it was also claimed. Two of them used French and German passports.
Hamas officials have so far failed to state why their commander was in Dubai, amid suggestions that he was on his way to Iran.
In a statement released last month, the militant group acknowledged that al-Mabhouh was involved in the kidnapping and killing of two Israeli soldiers in 1989, adding that until his death, he had played a "continuous role in supporting his brothers in the resistence inside the occupied homeland".
The Labour chair of the Commons Foreign Affairs Committee, Mike Gapes, said the case raised a "big concern" and backed the summoning of the ambassador if the UK suspected Israel.
"Clearly it raises a big concern. If another state - and we do not know it is definitely Israel - is using British passports, that is illegal."
Mr Gapes said the assassination was either carried out by Israel "or someone trying to make sure it looks like the Israelis".
"The level of sophistication and equipment... there are only a few countries that could do it.
"Israel has a record of assassinating Hamas leaders. They have a policy of targeted assassinations. It's possible (it was them)."
Asked about Sir Menzies' call, he said: "The British Government, if they are convinced it is Israel, should call the ambassador in."
The MP pointed out that Israeli agents had a record of using faked passports from friendly countries - and had assured Britain in 1986 that the practice would be halted.
Eight forged passports, and documents linking them with Israel, were discovered by chance in a German telephone booth and handed in to the British Embassy.
It was reported at the time that the then Israeli ambassador was given a dressing down by a Foreign Office minister and that an assurance was received that it would not happen again.
In the 1970s the British Government had complained to Israel after a female Mossad agent used a forged British passport to enter Beirut and murder a Palestinian leader suspected of masterminding the Munich Olympic Games massacre.Reuse content