* Move escalates rift over Doha ties to Muslim Brotherhood
* Powerful Arab states accuse Qatar of backing Iran agenda
* U.S. sees no impact on militant fight, urges resolution
* Egypt accuses Qatar of plan to sow discord
DUBAI, June 5 (Reuters) - 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 coordinated 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.
Announcing the closure of transport ties with Qatar, the three Gulf states gave Qatari visitors and residents two weeks to leave their countries. Qatar was also expelled from a Saudi-led coalition fighting in Yemen.
Economic disturbances loomed immediately, as Abu Dhabi's state-owned Etihad Airways said it would suspend all flights to and from Doha from Tuesday morning until further notice.
Oil giant Saudi Arabia accused Qatar of backing militant groups and broadcasting their ideology, in an apparent reference to Qatar's influential state-owned satellite channel al Jazeera.
"(Qatar) embraces multiple terrorist and sectarian groups aimed at disturbing stability in the region, including the Muslim Brotherhood, ISIS (Islamic State) 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 Shi'ite Muslim-populated Eastern region of Qatif and in Bahrain.
Qatar had no immediate reaction to the announcements, and Qatari officials could not be reached for comment, but it has denied supporting terrorism or Iran in the past.
WORLD CUP, U.S. BASE
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 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.
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 effect the fight against Islamist militants and that Washington has encouraged its Gulf allies to resolve their differences.
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 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 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.
(Additional reporting by William Maclean, Mohammed el-Sherif, Sylvia Westall and Amina Ismail; Editing by Sylvia Westall and Bill Tarrant)