Riyadh:Saudi Arabia, Egypt, Bahrain and the United Arab Emirates announced on Monday that they were severing diplomatic ties with Qatar, as tensions escalate in the region over the accusations that Doha sponsors terrorism.
Qatar, which has a population of 2.5 million people, is largely dependent on imported food to meet its needs.
Qatar reacted with fury, denying any support for extremists and accusing its Gulf neighbours of seeking to put the country under "guardianship".
Qatari diplomats in the UAE have been given only 48 hours to return home.
Egypt's government is fighting insurgencies by Isis and the Muslim Brotherhood, but Saudi Arabia has been accused of continuing to use al-Qaida as a proxy force in Syria and in internecine fighting with UAE-backed factions in Yemen.
Bahrain also prohibited its citizens from traveling to Qatar or residing in it and prohibited Qataris from entering Bahrain or passing through it. Founded in 1981, the GCC is a leading political and economic block in the Arab world. It appeared to be timed in concert with an earlier announcement by Bahrain similarly cutting ties.
At least seven countries cut diplomatic ties with Qatar on Monday over its alleged support of terrorism.
The abrupt decision has thrown the region into its greatest diplomatic crisis in decades and deepens a rift that has been growing for years between most of the Gulf states and Qatar.
Ties between Egypt and Qatar have been deteriorating since the ouster of the Egyptian Islamist-affiliated leader Mohamed Morsi in 2013 as a result of a mass protest against his rule.
Caught in the diplomatic crisis is the country's national airlines, Qatar Airways.
Qatar's Foreign Affairs Ministry said there was "no legitimate justification" for the countries' decision, though it vowed its citizens would not be affected by the "violation of its sovereignty".
Qatar is set to host the 2022 FIFA World Cup, and it is not clear if the world soccer governing body is going to take action after the latest move by the Gulf nations, following allegations that Doha is backing the Islamic States miltants, ISIS and al-Qaeda.
The coalition accused Qatar of providing "support to (terrorist) organisations in Yemen" - the first time it has made such a claim.
Although Qatar claims the posted comments were false, the country has always been seen by its neighbors as supporting Islamists in the region - particularly the Muslim Brotherhood, a Sunni Islamist political group outlawed by both Saudi Arabia and the UAE.
The world's no. 1 container shipping line Maersk said on Monday it was still open for business to and from Qatar, adding that it was following developments closely. And the Qatari airline Qatar Airways announced the termination of all flights to Saudi Arabia.