Stretching into the Persian Gulf from the beaches and skyscrapers of Dubai is a man-made archipelago in the shape of a vast palm tree, its branchlike rows of islands lined with luxury hotels, apartments and villas.

Among the owners of those homes are two dozen close allies of President Vladimir V. Putin of Russia, including a former provincial governor and nuclear power plant manager, a construction magnate and former senator, and a Belarusian tobacco tycoon.

At least 38 businessmen or officials linked to Mr. Putin own dozens of properties in Dubai collectively valued at more than $314 million, according to previously unreported data compiled by the nonprofit Center for Advanced Defense Studies. Six of those owners are under sanctions by the United States or the European Union, and another oligarch facing sanctions has a yacht moored there. For now, they can count themselves lucky.

Since the invasion of Ukraine, much of the world has imposed sweeping sanctions on Russian financial institutions and the circle around Mr. Putin, and even notoriously secretive banking centers like Switzerland, Monaco and the Cayman Islands have begun to cooperate with the freezing of accounts, seizing of mansions and impounding of yachts

But not Dubai, the cosmopolitan resort and financial center in the United Arab Emirates. Although a close partner to Washington in Middle Eastern security matters, the oil-rich monarchy has in recent years also become a popular playground for the Russian rich, in part because of its reputation for asking few questions about the sources of foreign money. Now the Emirates may undercut some of the penalties on Russia by continuing to welcome targeted oligarchs.

“Sanctions are only as strong as the weakest link,” said Adam M. Smith, a lawyer and former adviser to the U.S. Treasury Department office that administers such measures. “Any financial center that is willing to do business when others are not could provide a leak in the dike and undermine the overall measures.”

The Emirati stance is exposing tensions between the United States and several of its closest Arab allies over their reluctance to oppose the Russian invasion. Asked for solidarity in a moment of crisis, the United Arab Emirates, Saudi Arabia and Egypt have instead prioritized relations with Moscow — the Emirates and Saudi Arabia by rebuffing American pleas for increased oil supplies to soothe energy markets, Egypt by muffling criticism of the invasion while proceeding with a $25 billion loan from Russia to finance a nuclear power plant.

“It should be a clarifying moment,” said Michael Hanna, U.S. program director for the nonprofit International Crisis Group. “That has to be pretty bracing.”

The U.A.E. may be the most conspicuous in its position, if only because it currently holds a rotating seat on the United Nations Security Council. The Emiratis abstained from an American-backed resolution denouncing the invasion, declining to criticize Russia. And Emirati officials have reassured Russians that their authorities will not enforce sanctions unless mandated by the United Nations — where Moscow’s veto ensures against it.

“If we are not violating any international laws, then nobody should blame Dubai, or the U.A.E., or any other country for trying to accommodate whoever comes in a legitimate way,” said Abdulkhaleq Abdulla, a political analyst close to the U.A.E.’s rulers. “So what’s the big deal? I don’t see why the West would complain.”

Russians in Dubai say they appreciate the hospitality. “Having a Russian passport or Russian money now is very toxic — no one wants to accept you, except places like Dubai,” said a Russian businessman who took refuge there, speaking on the condition of anonymity for fear of alienating Emirati authorities. “There’s no issue with being a Russian in Dubai.”

He shared an electronic invitation circulating among Russians in the city: a rooftop cocktail party for venture capitalists and cryptocurrency start-ups. (The Treasury Department on Monday warned banks to watch for Russians using cryptocurrency to evade sanctions.)

An Arab businessman who rents high-end furnished apartments in Dubai described “incredible demand” from Russians since the invasion, with one family taking an indefinite lease on a three-bedroom waterfront apartment for $15,000 a month and more than 50 other individuals or families seeking accommodations.

The Center for Advanced Defense Studies, a Washington-based nonprofit that collects data on global conflicts, found that Putin allies owned at least 76 properties in Dubai, either directly or under the name of a close relative, and said that there were likely many others who could not be identified.

The center’s list of those under sanctions includes: Aleksandr Borodai, a Duma member who acted as prime minister of a Ukrainian province in 2014 when it was taken over by Russian-backed separatists; Bekkhan Agaev, a Duma member whose family owns a petroleum company; and Aliaksey Aleksin, the Belarusian tobacco titan. A handful of oligarchs on the list own homes valued at more than $25 million each

Maritime records show that in recent days the yacht belonging to the sanctioned oligarch Andrei Skoch, a steel magnate and Duma member, has been moored off Dubai.

A Bombardier business jet owned by Arkady Rotenberg, another Russian billionaire under sanctions, landed on Friday, and the planes and boats of other oligarchs discussed as possible targets have been coming and going, too. The yachts of at least three other oligarchs are currently docked in Dubai. The 220-foot vessel of a Russian metals magnate appears to be en route from the Seychelles. The Boeing 787 Dreamliner owned by Roman Abramovich, the Russian-born owner of Britain’s Chelsea soccer team, took off from the airport on Friday. A 460-foot superyacht belonging to another oligarch set sail the same day; he was added to Europe’s sanctions list on Wednesday.

Moscow has been quietly building closer ties to the U.A.E. and other Western-leaning Arab states for a decade, seeking to capitalize on complaints about Washington.

The autocrats who dominate the region were outraged by Washington’s statements of support for the Arab uprisings in 2011. The Arab monarchs of the Persian Gulf cried betrayal at the Obama administration’s deal with their adversary Iran over its nuclear program. Their frustration only grew when the Trump administration did nothing to retaliate for a series of apparent Iranian attacks against them.

Now people close to those rulers say that their neutral responses to the invasion of Ukraine should teach Washington not to take them for granted.

“The automatic expectation in D.C. is that ‘you Saudis now must jump on the bandwagon and isolate Russia as we have,’” said Ali Shihabi, a Saudi political analyst close to the royal court, but the kingdom cannot “burn” its relationship with Russia just to please the White House.

“Our relationship is there with the Americans,” he added, “but it is not going to be a monogamous relationship because the Americans are unreliable.”