DUBAI, United Arab Emirates -- Saudi Arabia and three other Arab countries severed ties to Qatar on Monday and moved to cut off land, sea and air routes to the energy-rich nation that is home to a major U.S. military base, accusing it of supporting regional terror groups.

Bahrain, Egypt, Saudi Arabia and the United Arab Emirates made no demands of Qatar as their decision plunged the international travel hub into chaos and ignited the biggest diplomatic crisis in the Gulf since the 1991 war against Iraq. The foreign minister for Libya's eastern-based government announced it would cut diplomatic relations with the country as well, and Al-Arabiya reported that the Maldives was making a similar move. Yemen's internationally recognized government, which no longer holds its capital and large portions of the country, cut relations with Qatar and said it supports the decision by the Saudi-led coalition to end Qatar's participation in the war on the Houthis there.

Qatar, which will host the 2022 FIFA World Cup and is home to some 10,000 American troops, criticized the move as a "violation of its sovereignty." It long has denied supporting militant groups and described the crisis as being fueled by "absolute fabrications" stemming from a recent hack of its state-run news agency.

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Saudi Arabia closed its land border with Qatar, through which the tiny Gulf nation imports most of its food, sparking a run on supermarkets. The four countries began withdrawing their diplomatic staff from Qatar as regional airlines announced they'd suspend service to its capital, Doha.

The move came just weeks after U.S. President Donald Trump visited Saudi Arabia and vowed to improve ties with both Riyadh and Cairo to combat regional terror groups and contain Iran. U.S. Secretary of State Rex Tillerson said the move was rooted in longstanding differences and urged the parties to resolve them.

Saudi Arabia said it took the decision to cut diplomatic ties due to Qatar's "embrace of various terrorist and sectarian groups aimed at destabilizing the region" including the Muslim Brotherhood, al-Qaida, the Islamic State of Syria and Iraq (ISIS) and groups supported by Iran in the kingdom's restive Eastern Province. Egypt's Foreign Ministry accused Qatar of taking an "antagonist approach" toward Cairo and said "all attempts to stop it from supporting terrorist groups failed."

The countries all ordered their citizens out of Qatar and gave Qataris abroad 14 days to return home to their peninsular nation, whose only land border is with Saudi Arabia. The countries also said they would eject Qatar's diplomats.

All the nations also said they planned to cut air and sea traffic. Doha-based satellite news network Al-Jazeera reported trucks carrying food had begun to line up on the Saudi side of the border, apparently stranded. The Qatar Stock Exchange fell more than 7 percent.

Qatar Airways, one of the region's major long-haul carriers that routinely flies through Saudi airspace, did not immediately respond to a request for comment. Some of its flights were going through Iranian airspace Monday. Saudi Arabia said it would begin blocking all Qatari flights at midnight.

Qatar's Foreign Affairs Ministry said there was "no legitimate justification" for the countries' decision, though it vowed its citizens wouldn't be affected by it.

"The Qatari Government will take all necessary measures to ensure this and to thwart attempts to influence and harm the Qatari society and economy," it said.

Premier UAE airlines Etihad and Emirates announced they would suspend flights to Qatar, as did budget carriers Air Arabia and FlyDubai. Bahrain's Gulf Air and Saudia joined them.

Saudi Arabia also said Qatari troops would be pulled from the ongoing war in Yemen. Yemen's internationally backed government, which no longer holds its capital and large portions of the country, also cut relations with Qatar, as did the Maldives. FIFA, international soccer's governing body, said it remained in regular contact with Qatar, declining to elaborate.

Qatar is home to the sprawling al-Udeid Air Base, which is home to the forward headquarters of the U.S. military's Central Command. It wasn't clear if the decision would affect American military operations. Central Command officials and the Pentagon did not immediately respond to a request for comment.

In Sydney, Tillerson said he didn't believe the diplomatic crisis would affect the war against the Islamic State group in Iraq and Syria.

"I think what we're witnessing is a growing list of disbelief in the countries for some time, and they've bubbled up to take action in order to have those differences addressed," he said. "We certainly would encourage the parties to sit down together and address these differences."

Before Monday, Qatar had appeared unperturbed by the growing tensions. On May 27, Qatar's ruling emir, Tamim bin Hamad Al Thani, called Iranian President Hasan Rouhani to congratulate him on his re-election.

The call was a clear, public rebuttal of Saudi Arabia's efforts to force Qatar to fall in line against the Shiite-ruled nation, which the Sunni kingdom sees as its No. 1 enemy and a threat to regional stability. Qatar shares a massive offshore gas field with Iran.

The crisis began in late May when Qatar alleged that hackers took over the site of its state-run news agency and published what it called fake comments from its ruling emir about Iran and Israel. Its Gulf Arab neighbors responded by blocking Qatari-based media, including Al-Jazeera.

Qatar long has faced criticism from its Arab neighbors over its support of Islamists. The chief worry among them is the Muslim Brotherhood, a Sunni Islamist political group opposed to monarchical rule.

Gulf countries led by Saudi Arabia fell out with Qatar over its backing of Egyptian President Mohammed Morsi, a Brotherhood member who was overthrown by the military in 2013. In March 2014, Saudi Arabia, the United Arab Emirates and Bahrain recalled their ambassadors from Qatar over the rift. Eight months later, they returned their ambassadors as Qatar forced some Brotherhood members to leave the country and quieted others.

Qatar denies funding extremist groups. However, it remains a key patron of the Islamic Hamas movement, which rules the Gaza Strip. Western officials also have accused Qatar of allowing or even encouraging funding of Sunni extremists like al-Qaida's branch in Syria, once known as the Nusra Front.

Mr. Trump nevertheless met with Qatar's emir during the Saudi conference last month.

"We are friends, we've been friends now for a long time, haven't we?" Mr. Trump asked at the meeting. "Our relationship is extremely good."