London, England (CNN) -- British citizens who travel to Israel should be aware that their passport details could be captured for "improper uses," Britain's Foreign Office warned Tuesday.
It follows Britain's expulsion of an Israeli diplomat and its accusation that the Israeli government was responsible for forging British passports used in an international murder plot.
Foreign Secretary David Miliband said Tuesday that there are "compelling reasons" to believe Israel was behind it.
Twelve suspects in the January murder of Hamas leader Mahmoud al-Mabhouh, who was found dead in his Dubai hotel room, used British passports, the Dubai police have said.
Miliband said the passports had been copied from "genuine British passports" in a "highly sophisticated operation," indicating that a state intelligence service was responsible.
The Foreign Office changed its official travel advice Tuesday for British citizens going to Israel, to warn them about the risk of their passport details being compromised.
A British investigation "found circumstantial evidence of Israeli involvement in the fraudulent use of British passports," the advice says. "This has raised the possibility that your passport details could be captured for improper uses while your passport is out of your control. The risk applies in particular to passports without biometric security features.
"We recommend that you only hand your passport over to third parties, including Israeli officials, when absolutely necessary."
Britain's Serious Organised Crime Agency concluded that the 12 British people whose passports were cloned were "wholly innocent victims of identity theft," the foreign secretary said.
Israel has a stated policy on security matters of neither confirming nor denying involvement.
Australian Foreign Minister Stephen Smith said the British government would be giving its report on the passports to the Australian Federal Police, who are investigating how some of their country's passports came to be used by the Dubai suspects.
In an interview Tuesday with the Australian Broadcasting Company, Smith said Australia was not taking any action yet.
"We have an investigation underfoot, and we will await the results of that investigation by the Australian Federal Police," Smith said.
He added: "We're treating this matter very seriously. Israel understands that, and when I receive the report (from the federal police), we'll make judgments which will be in Australia's national interest."
Dubai police had previously said three Australian passports were used in the murder plot, but Smith said there were four. He said there is nothing to indicate that the holders of the passports were anything but "innocent victims" in the crime.
Al-Mabhouh, a founding member of Hamas' military wing, was found dead January 20 in his Dubai hotel room. Police believe he was killed the night before, allegedly by the secretive Israeli foreign intelligence unit Mossad.
A source close to the investigation said Wednesday that the total number of suspects had increased to 28, from 27, after Australia confirmed the use of a fourth passport.
Six suspects used Irish passports, four used French documents, one had German papers and four had Australian papers. There is also one Palestinian suspect, police have said.
Lt. Gen. Dahi Khalfan Tamim, Dubai police chief, has said not all the suspects had fraudulent passports. "We know some of the names are real," he said.
Interpol, the international police agency, has issued "red notices" to help search for the suspects. The notices are not international arrest warrants, but are a way of alerting police forces around the world that the suspects are wanted by United Arab Emirates authorities.