Saudi, Egypt, Bahrain and UAE cut relations with Qatar
In what appears to be a coordinated move, foreign office officials claimed Qatar was responsible for supporting the Islamic State group and al-Qaeda "at all levels" in an unprecedented diplomatic spat for the Gulf region.
The land border with Saudi Arabia has also reportedly been sealed.
In a tweet sent out early on Monday morning, the Saudi Ministry of Foreign Affairs said: "Protecting national security from threats of terrorism and extremism, Saudi Arabia has decided to sever diplomatic and consular relations with the State of Qatar."
In a statement published by Qatar’s foreign ministry, authorities said the decision, which it claims was clearly pre-meditated, “is based on baseless fabricated claims.”
“Qatar has been the target of a systematic incitement campaign that promoted outright lies which indicates that there was a prior intent to harm the state,” the statement said.
Riyadh announced on state television that Qatar would no longer participate in the Saudi-led coalition in Yemen, claiming Doha it had helped support its enemy, al-Qaeda in the Arabian Peninsular. The Saudi-led campaign in Yemen's war has mostly targeted Iran-backed Houthi rebels, who are supported by Yemen's ousted president, Ali Abdullah Saleh.
Saudi Arabia was the first country to break off relations at just after 3.30am GMT, followed shortly by Bahrain, Egypt and the UAE.
Riyadh also announced closures to Qatar's only land border - with Saudi Arabia - and gave diplomatic staff 48 hours to leave the country.
The UAE also announced its citizens would no longer be allowed to visit Doha.
UAE state media agency said the Emirates "regretted Qatar's policies had driven a wedge between them", but confirmed its "respect and appreciation to our brother people".
Monday's diplomatic incident is the latest in a series of events related to Saudi Arabia's opposition to Qatar's alleged support for the Muslim Brotherhood.
The Saudi foreign minister, Adel al-Jubeir, held talks with his Egyptian counterpart in Cairo on Sunday, discussing a joint approach to fighting regional terrorism.
The two ministers said they had "full compatibility of views".