Saudi Arabia, Egypt, the United Arab Emirates and Bahrain severed their ties with Qatar on Monday, accusing it of supporting terrorism, in an unprecedented breach between the most powerful members of the Gulf Cooperation Council.
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.
The three Gulf States and Egypt announced the closure of transport ties with Qatar and gave Qatari visitors and residents two weeks to leave their countries. Qatar was also expelled from a Saudi-led coalition fighting in Yemen.
These were more severe measures than during a previous eight-month rift in 2014, when Saudi Arabia, Bahrain and the UAE withdrew their ambassadors from Doha. 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.
Qatar is also due to host the World Cup in 2022.
In a statement on state news agency SPA, oil giant Saudi Arabia accused Qatar of backing militant groups and spreading their violent 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 and al-Qaeda, and promotes the message and schemes of these groups through their media constantly," 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.
There was no immediate Qatari reaction to the announcements, and Qatari officials could not be reached for comment, but it has denied supporting terrorism or Iran in the past.
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."