In Israel's quest for normal ties with the Arab world, the United Arab Emirates has been among the few countries to offer a slight opening. It allowed an Israeli cabinet minister to attend an energy conference, let an Israeli tennis star play in a recent tournament, and offered a wink and a welcome to Israelis arriving with U.S., European or other third-country passports.

That window closed a bit on Monday as Dubai officials -- angered about the killing of a Hamas operative, which they blame on Israeli undercover agents -- said they would now be on the lookout for Israelis, regardless of what travel documents they hold. Gen. Khalfan Tamim, the emirate's police chief, told reporters at a security conference that "among the things we will train our people [to do] is to identify Israeli names, accents as well as features."

"We knew Israelis from their accents, but when they used European passports to come here, we accepted that and we treated them as Europeans," Tamim said. "But after this day, if they have dual citizenship, we will exert extreme caution."

Tamim continued to publicly detail evidence in a case that began as a cloak-and-dagger tale involving fake beards and wigged assassins but has grown into an enlarging diplomatic problem for Israel.

Agents from Britain's Serious Organized Crime Agency are in Israel investigating the use of forged British passports by people who Dubai officials allege were part of an assassination squad run by Israel's Mossad spy agency. The 27 members of the group used European or Australian passports -- some forged -- to enter Dubai, officials say. In several cases, the names and other information on the passports matched those of Israeli citizens who hold dual nationality and who claim that their identities were "borrowed" by those involved in the operation.

Two SOCA agents will interview the 10 British-Israelis who were affected and issue them new passports, a British Embassy spokesman said. According to Israeli news reports, Australian investigators are planning a similar visit. The European Union last week condemned the use of forged travel documents in the killing of Hamas commander Mahmoud al-Mabhouh, without mentioning Israel specifically.

Tamim and other Dubai officials have used a series of news conferences to sustain focus on the case in Israel and internationally -- releasing photos of the suspects and video from security cameras, diagramming their convergence in Dubai from points around the world and their exit to disparate locales, and this week disclosing toxicology reports showing that Mabhouh had been injected with a muscle relaxant before being suffocated. The fast-acting drug succinylcholine would have weakened him and, according to descriptions of the chemical on medical Web sites, could also contribute to respiratory failure.

Israel has maintained a steady silence in the case -- in contrast with the government's quick rebuttal to other perceived diplomatic slights. The country is facing what some officials regard as a deep image crisis, stemming in part from the stalled Israeli-Palestinian peace process and from criticism that the country used excessive force in a three-week war a year ago in Hamas's stronghold, the Gaza Strip.

Mabhouh, a founder of the militant group's armed wing, was involved in the killing of two Israeli soldiers in the 1980s and more recently is suspected of being a key conduit of arms to Gaza.

Israel has adopted a "policy of ambiguity" when it comes to confirming or denying suspicions about its Mossad spy agency. The organization has a documented record of using the passports of other countries in its undercover operations -- a virtual necessity given the inability of Israeli passport holders to enter many Arab countries. The United Arab Emirates maintains no diplomatic relations with Israel and does not honor Israeli passports.

When Israeli officials have commented on Mabhouh's case, they have tended to focus on what they consider the strategic benefit of his death.

"What is there to criticize here?" cabinet member Binyamin Ben-Eliezer told Israel's Army Radio on Sunday. "I see only one simple thing here: whether he is alive or dead."