Egypt, Saudi Arabia and three other Arab countries severed all ties with Qatar early Monday, in a renewal of a four-year effort to isolate it and in a sign of a new boldness after a visit to the region by President Trump.
In an abrupt and surprising move, the five Arab states not only suspended diplomatic relations, as they have in the past, but also cut off land, air and sea travel to and from Qatar. All but Egypt, which has many thousands of people working there, ordered their citizens to leave the country.
Qatar, like other monarchies in the Persian Gulf, is a close ally of Washington, and it hosts a major American military base that commands the United States-led air campaign against the Islamic State.
As such, the feud among regional allies threatens to stress the operations of the American-led coalition and complicate efforts in the region to confront Iran — but could also be a heavy blow to Tehran’s regional ambitions, if Qatar is forced to sever ties.
Secretary of State Rex W. Tillerson offered to broker the impasse on Monday in the hope of preserving the Trump administration’s efforts to create broad coalitions against Iran and terrorist groups in the Middle East.
“We certainly would encourage the parties to sit down together and address these differences,” Mr. Tillerson said.
The severing of all connections by Bahrain, Egypt, Saudi Arabia, the United Arab Emirates and Yemen created an immediate crisis for Qatar. Qatari diplomats were given 48 hours to leave their posts in Bahrain, while Qatari citizens were allotted two weeks to depart Bahrain, Saudi Arabia and the United Arab Emirates.
Qatar, a relatively small country jutting into the Persian Gulf, has a border with Saudi Arabia and is vulnerable to its larger neighbor. It imports almost all of its food, about 40 percent of it directly from Saudi Arabia. Several residents, reached on the internet chat, said that people were stocking up on food and cash.
Air traffic was disrupted, with the United Arab Emirates suspending service to Qatar by its three carriers, Etihad Airways, Emirates and FlyDubai, beginning Tuesday morning. Qatar Airways was banned from Saudi airspace.
Saudi Arabia said it was taking the action to “protect its national security from the dangers of terrorism and extremism.” The Foreign Ministry of Qatar released a statement saying the action had “no basis in fact” and was “unjustified.”
The Iranian government criticized the Saudi-led action against Qatar in a diplomatically worded rebuke. “Neighbors are permanent; geography can’t be changed,” Foreign Minister Mohammad Javad Zarif said on his Twitter account. “Coercion is never the solution,” Mr. Zarif said. “Dialogue is imperative, especially during blessed Ramadan.”
It was not immediately clear why the five countries decided to take this action now. Last month, Qatar’s state news media published comments attributed to the emir, Sheikh Tamim bin Hamad al-Thani, referring to tension with Washington over Iran policy and saying Mr. Trump might not be in power for long. Qatar denied the comments, saying it had been the victim of a “cybercrime.”
But most analysts pointed to President Trump’s recent visit to Saudi Arabia.
Yezid Sayigh, a senior fellow at the Carnegie Middle East Center in Beirut, Mr. Sayigh said that the new moves reflected a “bullishness” prompted by the Trump administration’s stances — on the confrontation with Iran and on a willingness to look the other way on human rights violations.
Saudi Arabia and the United Arab Emirates are getting “no U.S. pushback” on human rights or on the Yemen intervention, he said, while “Egypt also feels off the hook with Trump, and is using the opportunity to repair ties with the Saudis, reinforce with the Emiratis and be more assertive in Libya.”
But the move also creates potential complications for the United States — raising questions about whether the Trump administration knew it was happening; if they understood the pitfalls; if they attempted to counter it and could not.
“The question is what if anything will this administration do about it?” said Randa Slim, a regional analyst at the Middle East Institute in Washington. “Was it forewarned and did not have the staffing needed to mount an intelligent pre-emptive action? Going forward, will the U.S. put brakes on the escalation path? Or let it move forward?”
She said that an escalation against Qatar was not a surprise given the brewing tension: “Regionally, the decks are stacked against Qatar. If denied U.S. support, the Qatari emir has no option but to back down.”
But the move carries perils for the other countries as well, Mr. Sayigh warned. “Cutting relations with Qatar suggests a worrying readiness to be assertive and belligerent,” he said. which masks the countries’ deeper problems and challenges and may prove to be a case of overreach.”
In another indication of how the Trump visit may have emboldened Gulf monarchies, Bahrain has cracked down on opposition from its Shiite majority over the last two weeks.
Qatar, one of the richest countries in the world, has used that wealth in recent years to play an outsize role in regional politics. It has often sought to be the honest broker, trying to mediate the region’s intractable conflicts. But just as often, it has ended up angering all sides.
Its actions are a study in contradictions. Qatar has good relations with Iran, but hosts the American air base, is helping to fight the Iranian-backed Houthi rebels in Yemen and supports insurgents against the Syrian government of President Bashar al-Assad, which is backed by Tehran. And yet, the Qatari emir once gave Mr. Assad an Airbus plane.
Home to some Israeli officials, Qatar has also given refuge to Khaled Mashal, a leader of Hamas, the hard-line Islamist group in Gaza that advocates the destruction of Israel.
Tensions had been building for years, beginning with Qatar’s support for the Muslim Brotherhood in Egypt and through the broadcasts of the Pan-Arab news network Al Jazeera, which Qatar funds. Qatar’s rivals have also faulted it for condoning fund-raising for militant Islamist groups fighting in Syria, although several of the other Sunni-led monarchies in the region have played similar roles.
Qatar’s opponents have recently added a third allegation to those grievances: that it is conspiring with their regional rival, Iran. That latest charge is especially striking given Qatar’s role in the fighting against the Houthis in Yemen and the Assad government.
Qatar has had its successes. It has taken an important back-channel role with Iran to defuse points of contention in the Syrian war. It has repeatedly brokered hostage and prisoner exchanges, paying millions of dollars to insurgent groups in the deals.
Qatar is also a sponsor of the Four Towns agreement in Syria, negotiated with Iran and Hezbollah, in which civilians trapped under siege by government troops or by rebel forces have been bused to other areas. The deals are hailed by some as the only way to rescue civilians, but they have been derided by others as forced displacements.
However the crisis is resolved, if at all, Mr. Tillerson and Defense Secretary Jim Mattis, who appeared in their first joint news conference, in Sydney, Australia, after talks with their Australian counterparts, insisted that it would not undermine the fight against the Islamic State, also known as ISIS or ISIL.
“I am confident there will be no implications,” Mr. Mattis said.
But the escalating confrontation between Qatar and other Sunni-led Arab states presents a fresh and unwelcome complication for the United States military, which has made strenuous efforts to forge a broad coalition against the Islamic State.
How, for example, can the American-led air campaign include warplanes from Bahrain, Saudi Arabia and the United Arab Emirates if those governments will no longer allow their military representatives to be based at, or even to visit, a major United States command center?
Beyond the military difficulties, several multinational corporations have operations in the feuding nations. A Saudi call for companies to withdraw from Qatar could present international executives with a difficult choices about where to do business.
Qatar is hosting the 2022 World Cup, for instance, and is building facilities for the tournament that are part of an ambitious construction boom, including creating branches of major international museums and universities.
About 80 percent of Qatar’s residents are foreign workers, including white-collar professionals and construction and service workers. There are several hundred thousand Egyptians working in Qatar, which is perhaps why Cairo did not call for its citizens to leave like Saudi Arabia did.