RIYADH (AFP, REUTERS) - Arab nations including Saudi Arabia and Egypt on Monday (June 5) cut ties with Qatar accusing it of supporting extremism, in the biggest diplomatic crisis to hit the region in years.

Bahrain, the United Arab Emirates and Yemen joined Saudi Arabia and Egypt in severing relations with gas-rich Qatar, with Riyadh accusing Doha of supporting groups, including some backed by Iran, "that aim to destabilise the region".

Qatar reacted with fury, denying any support for extremists and accusing its Gulf neighbours of seeking to put the country under "guardianship".

The crisis was likely to have wide-ranging consequences, not just for Qatar and its citizens but around the Middle East and for Western interests.

Qatar hosts the largest US airbase in the region, which is crucial to operations against Islamic State in Iraq and Syria (ISIS) group extremists, and is set to host the 2022 football World Cup.

Monday's announcement came less than a month after US President Donald Trump visited Saudi Arabia to cement ties with Riyadh and called for a united front among Muslim countries against extremism. It also followed weeks of rising tensions between Doha and its neighbours, including Qatari accusations of a concerted media campaign against the country and the alleged hacking of the Qatar News Agency.

Qatar slams 'baseless claims'

Qatar said it was facing a campaign of lies and fabrications aimed at putting the Gulf Arab state under guardianship.

"The campaign of incitement is based on lies that had reached the level of complete fabrications," the Qatari foreign ministry said.

It added that, as a member of the Gulf Cooperation Council, it was committed to its charter, respected the sovereignty of other states and did not interfere in their affairs.

Saudi Arabia, the United Arab Emirates, and Bahrain earlier on Monday announced the closure of transport ties with Qatar and gave Qatari visitors and residents two weeks to leave their countries. Yemen followed suit hours later.

The coordinated move by the three Gulf states as well as Egypt dramatically escalates a simmering 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.

Saudi Arabia accused Qatar of backing militant groups and spreading their violent ideology, in an apparent reference to its influential state-owned satellite channel Al-Jazeera. Qatar has denied supporting terrorism or Iran in the past.

"(Qatar) embraces multiple terrorist and sectarian groups aimed at disturbing stability in the region, including the Muslim Brotherhood, ISIS (Islamic State in Iraq and Syria) and Al-Qaeda, and promotes the message and schemes of these groups through their media constantly," state news agency SPA said.

The statement went on to accuse Qatar of supporting what it described as Iranian-backed militants in its restive and largely Shi'ite Muslim-populated Eastern region of Qatif and in Bahrain.

On its state news agency, Egypt, the Arab world's most populous nation, said 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."

Yemen also said in a statement it supported the decision to expel Qatar from the Saudi-led Arab coalition backing President Abedrabbo Mansour Hadi's government against Shi'ite rebels. It accused Doha of "dealing with the insurgent militias and supporting extremist groups in Yemen, which contradicts the aims agreed upon by states supporting Yemen's legitimate government."

Qatar's air force and troops participated in the Arab coalition that launched a military campaign against Iran-backed Huthi rebels in March 2015, when they closed in on Hadi's refuge in the southern city of Aden.

World Cup, US base

Iran - long at odds with Saudi Arabia and a behind-the-scenes target of the move - immediately blamed US President Donald Trump for setting the stage during his recent trip to Riyadh.

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.

A split between Doha and its closest allies can have repercussions around the Middle East, where 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 US 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.

Kristian Ulrichsen, a Gulf expert at the US-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.

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

"We certainly would encourage the parties to sit down together and address these differences," he said in Sydney. "If there's any role that we can play in terms of helping them address those, we think it is important that the GCC (Gulf Cooperation Council) remain united."

The announcements come 10 days after President Donald Trump visited Riyadh to call on Muslim countries to stand united against Islamists 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 US-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."

Break not helpful, says Iran

A senior Iranian official said on Monday the decision by some Gulf Arab states and Egypt to sever diplomatic ties with Qatar would not help end the crisis in the Middle East.

"The era of cutting diplomatic ties and closing borders ... is not a way to resolve crisis ... As I said before, aggression and occupation will have no result but instability," Hamid Aboutalebi, deputy chief of staff of Iran's President Hassan Rouhani, tweeted on Monday.

'Arab Spring'

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 backfoot in the region, especially after a 2013 military takeover in Egypt ousted the elected Islamist president.

The former army chief and now president, Abdel Fattah al-Sisi, 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.