CAIRO — Tensions between Qatar and neighboring Persian Gulf monarchies broke out Wednesday when Saudi Arabia, the United Arab Emirates and Bahrain withdrew their ambassadors from the country over its support of the Muslim Brotherhood and allied Islamists around the region.

The concerted effort to isolate Qatar, a tiny, petroleum-rich peninsula, was an extraordinary rebuke of its strategy of aligning with moderate Islamists in the hope of extending its influence amid the Arab Spring revolts.

But in recent months Islamists’ gains have been rolled back, with the military takeover in Egypt, the governing party shaken in Turkey, chaos in Libya and military gains by the government in Syria.

The other gulf monarchies had always bridled at Qatar’s tactic, viewing popular demands for democracy and political Islam as dual threats to their power.

The Saudi monarchs, in particular, have grumbled for years as tiny Qatar has swaggered around like a heavyweight. It used its huge wealth and Al Jazeera, which it owns, as instruments of regional power. It negotiated a peace deal in Lebanon, supported Palestinian militants in Gaza, shipped weapons to rebels in Libya and Syria, and gave refuge to exiled leaders of Egypt’s Brotherhood — all while certain its own security was assured by the presence of a major American military base.

Wednesday’s breach, some in the region said, was Qatar’s comeuppance. “The other gulf states see Qatar as this extremely rich child that has got all this money and all these big toys and wants to play but doesn’t know how to do it,” said Michael Stephens, a researcher in Doha, Qatar’s capital, for the London-based Royal United Services Institute.

For the West, this latest twist in the heated politics of the region divides close allies at a critical time. All four gulf countries actively back the Syrian rebels against President Bashar al-Assad, and all see Shiite Iran as a regional rival. But now the split with Qatar makes it harder for the West to work with them as a group on common concerns like Iran or Syria.

In addition to differences over Sunni groups like the Brotherhood, Qatar also views Iran as a manageable concern, while Saudi Arabia sees it as an existential danger, analysts said. The internal tensions make it harder for Washington to reassure the nervous governments in the United Arab Emirates and Saudi Arabia that American negotiations with Iran over its nuclear program will not undermine gulf security. And a diplomatic breakdown like the withdrawal of the ambassadors all but precludes any hope of coordinating their competing efforts to bolster the Syrian rebels, another Western goal.

“The gulf squabbling really does not help,” Mr. Stephens said. Iran, he said, is “the only one who wins from this.”

In a joint statement, Saudi Arabia, the United Arab Emirates and Bahrain all but accused Qatar of engaging in espionage against them by supporting the Brotherhood and providing a media platform for its allies.

The statement said they had withdrawn their envoys “to protect their security” because Qatar failed to fulfill vows “to refrain from supporting organizations or individuals who threaten the security and stability of the gulf states, through direct security work or through political influence,” and also “to refrain from supporting hostile media.”

But after “strenuous attempts” at a meeting of their representatives at the Gulf Cooperation Council in Riyadh, Saudi Arabia, on Tuesday night, the statement said, Qatar still “declined to commit to enforce these measures.”

In its own statement, Qatar expressed “surprise and regret” and denied that the rift had anything to do with “security and stability.”

The other gulf states were retaliating against Qatar for refusing to join them in backing the military ouster of Egypt’s Islamist president by Abdul-Fattah el-Sisi, now a field marshal, said Nasser bin Hamad M. al-Khalifa, a former Qatari ambassador to Washington, speaking on Al Jazeera’s English-language network. “The whole issue is really about Sisi,” he said. “These countries are supporting a coup d’état” and “they want Qatar to support such a policy” but “we will never support another regime that kills its own people.”

He said Saudi Arabia, the United Arab Emirates and Bahrain were trying to take the Arab world back to the years before the Arab Spring of 2011. “They want to keep the Arab world in the hole, they want them to stay weak countries controlled by dictators,” he said, but “we are not going to support dictators.”

Tensions between Qatar and Saudi Arabia go back further. In 2002, Saudi Arabia withdrew its ambassador in protest over broadcasts by Al Jazeera that included criticism of the kingdom and its founder; the ambassador did not return until 2007.

But it is the battle for Egypt that has brought tensions between Qatar and its neighbors to a new peak. Saudi Arabia and the United Arab Emirates have cheered Field Marshal Sisi for removing the Islamists from power in Cairo before their example or influence might stir unrest closer to home. Both lavished Egypt’s new military-backed government with critical financial support, and both nodded approvingly when it outlawed the Brotherhood as a terrorist group.

Qatar, on the other hand, was Egypt’s most important donor when the Brotherhood was in power. Doha, along with London and Istanbul, has become a hub for Brotherhood leaders in exile.

And Al Jazeera has continued to provide the only Arabic-language news coverage in Egypt sympathetic to the Brotherhood even as Egypt’s government has begun treating the network itself as something close to a terrorist group, including jailing four of its journalists.

Perhaps most gallingly to Saudi Arabia and the United Arab Emirates, Al Jazeera has provided a platform for Sheik Yusuf al-Qaradawi, an influential Egyptian-born preacher close to the Brotherhood, as he has fiercely criticized the gulf governments for backing the military takeover.

The United Arab Emirates state news media reported last month that its government had summoned Qatar’s ambassador to express “extreme resentment” at a declaration on Al Jazeera by Sheik Qaradawi that the Emirates “has always been opposed to Islamic rule.”

But even the summoning of the ambassador did not persuade the Qataris to keep Sheik Qaradawi from returning with more criticism the next week, said Mustafa Alani, a scholar at the Gulf Research Center in Geneva. And the Saudis and Emiratis objected that Qatar did not join Egypt in declaring the Brotherhood a terrorist threat, he said.

“Qatar has never hidden their support of the Muslim Brotherhood,” Mr. Alani said. “In all the other countries, Qaradawi and his like are on the black list, but the Qataris give this man a platform to attack and criticize the security policies of the other states” in the gulf.

“The Qataris are not toeing the line,” he said.