Saudi Arabia, Egypt, the United Arab Emirates and Bahrain severed their ties with Qatar on Monday, accusing it of supporting terrorism, opening up the worst rift in years among some of the most powerful states in the Arab world. 

The co-ordinated move dramatically escalates a dispute over Qatar's support of the Muslim Brotherhood, the world's oldest Islamist movement, and adds accusations that Doha even backs the agenda of regional arch-rival Iran.

The countries ordered their citizens out of Qatar and gave Qataris abroad 14 days to return home. The countries also said they would eject Qatar's diplomats from their territories. Some Egyptian banks halted all dealings with Qatari banks.

Saudi Arabia closed its land border with Qatar, through which the tiny Persian 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, starting Tuesday.

Qatar was also expelled from a Saudi-led coalition fighting in Yemen.

The Maldives later said it too was severing diplomatic ties "because of its firm opposition to activities that encourage terrorism and extremism," according to a statement from the government of the tiny Indian Ocean archipelago nation.

Yemen's internationally backed government, which no longer holds its capital and large portions of the country, also cut relations with Qatar.

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

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. 

Flights suspended

However, the crisis immediately wreaked havoc with its long-haul carrier Qatar Airways, sent the Qatari stock market tumbling and raised questions about how a country reliant on food imports would be affected. 

Qatar's state-owned satellite news channel 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 seven per cent.

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. 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.

Oil giant Saudi Arabia accused Qatar of backing militant groups and broadcasting their ideology, in an apparent reference to Al-Jazeera.

Qatar

A Qatari employee of Al-Jazeera's Arabic-language TV news channel walks past its logo in Doha. Saudi Arabia accused Qatar of backing militant groups and broadcasting their ideology. (Kamran Jebreili/Associated Press)

"[Qatar] embraces multiple terrorist and sectarian groups aimed at disturbing stability in the region, including the Muslim Brotherhood, ISIS and al-Qaeda, and promotes the message and schemes of these groups through their media constantly," the Saudi state news agency SPA said.

The statement accused Qatar of supporting what it described as Iranian-backed militants in its restive and largely Shia Muslim-populated Eastern region of Qatif and in Bahrain.

World Cup host

The measures are more severe than during a previous eight-month rift in 2014, when Saudi Arabia, Bahrain and the UAE withdrew their ambassadors from Doha, again alleging Qatari support for militant groups.

At that time, travel links were maintained and Qataris were not expelled.

The current 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 neighbours responded by blocking Qatari-based media, including Al-Jazeera.

A split between Doha and its closest allies can have repercussions around the Middle East, where Persian Gulf states have used their financial and political power to influence events in Libya, Egypt, Syria, Iraq and Yemen.

The diplomatic broadside threatens the international prestige of Qatar, which hosts a large U.S. military base and is set to host the 2022 World Cup. It has for years presented itself as a mediator and power broker for the region's many disputes.

International soccer's governing body says it remains in "regular contact with Qatar" amid the crisis.

FIFA issued a short statement Monday saying it spoke with the World Cup organizing and operations committees, and said, "We have no further comments for the time being."

Could wreak havoc

Kristian Ulrichsen, a Gulf expert at the U.S-based Baker Institute, said if Qatar's land borders and air space were closed for any length of time "it would wreak havoc on the timeline and delivery" of the World Cup.

U.S. Secretary of State Rex Tillerson told reporters in Sydney on Monday that the spat would not affect the fight against Islamist militants and that Washington has encouraged its Gulf allies to resolve their differences.

The announcements come 10 days after U.S. President Donald Trump visited Riyadh to call on Muslim countries to stand united against Islamist extremists, and singling out Iran as a key source of funding and support for militant groups.

"It seems that the Saudis and Emiratis feel emboldened by the alignment of their regional interests — toward Iran and Islamism — with the Trump administration," said Kristian Ulrichsen, a Gulf expert at the U.S-based Baker Institute.

"[They] have decided to deal with Qatar's alternative approach on the assumption that they will have the [Trump] administration's backing."

Qatar's Emir Sheikh Tamim bin Hamad Al-Thani met with Trump in Riyadh last month. 

Muslim Brotherhood on its back foot

Qatar has used its media and political clout to support long-repressed Islamists during the 2011 pro-democracy "Arab Spring" uprisings in several Arab countries.

Muslim Brotherhood parties allied to Doha are now mostly on the back foot in the region, especially after a 2013 military takeover in Egypt ousted the elected Islamist president.

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Al-Thani met with U.S. President Donald Trump in Riyadh, Saudi Arabia, last month. (Jonathan Ernst/Reuters)

The former army chief and now president, Abdel-Fattah el-Sissi, along with the new government's allies in Saudi Arabia and the UAE, blacklist the Brotherhood as a terrorist organisation.

Egypt, the Arab world's most populous nation, said on its state news agency that Qatar's policy "threatens Arab national security and sows the seeds of strife and division within Arab societies according to a deliberate plan aimed at the unity and interests of the Arab nation."

Oil prices rose after the moves against Qatar, which is the biggest supplier of liquefied natural gas (LNG) and a major seller of condensate — a low-density liquid fuel and refining product derived from natural gas. Qatar Petroleum was still seeking gasoil from countries in the Gulf Cooperation Council (GCC) even after some members of the group severed ties with the country, two trading sources said on Monday.

With files from The Associated Press