Saudi Arabia, Egypt, the United Arab Emirates, Bahrain and Yemen have cut diplomatic ties with Qatar over alleged terrorism and national-security concerns.
Joined by the Maldives and the government of eastern Libya, they accuse Qatar of harbouring banned groups such as al-Qaeda and IS in an effort to erode stability in the Middle East.
Qatar claims its neighbours want to introduce guardianship of the state in violation of its sovereignty, that they never raised the issue at the Gulf Cooperation Council meeting.
Foreign Minister Sheikh Mohammed bin Abdulrahman Al Thani has told Al Jazeera the claims are false and designed to destabilise Qatar.
"Are there any other reasons? If there were other reasons behind this crisis, if there were real reasons, it would have been put on the table for discussion during the GCC meeting. And we were there at the meeting for the GCC, and none of that was mentioned. (Nothing) was said about tension in the intra-Gulf relations. And it wasn't mentioned either during the American-Islamic-Arab summit in Riyadh. There were no indications whatsoever."
The countries have given Qatar's diplomats 48 hours to return home, and its nationals have two weeks to leave -- except those living in Egypt are allowed to stay.
Land, air and sea travel bans are causing major disruptions.
Qatar has also been expelled from the Saudi-led military coalition bombing Yemen.
And there are fears about the impact of border closures on the food supply in the Persian Gulf state, due to a heavy reliance on Saudi imports.
The United States, which has a military base in Qatar, has offered its help.
Secretary of State Rex Tillerson has urged the nations involved to find a diplomatic solution.
"We certainly would encourage the parties to sit down together and address these differences. And if there's any role that we can play in terms of helping them address those, then we think it is important that the GCC remain unified. I do not expect that this will have any significant impact, if any impact at all, on the unified fight against terrorism in the region or globally."
China's foreign-ministry spokeswoman, Hua Chunying, has echoed calls from Turkey and Russia as well for the Gulf states to sort things out.
"The Chinese side hopes relevant countries could handle their differences properly through dialogue and consultation and work together to safeguard solidarity and promote peace and stability in the region."
The move is seen as a major diplomatic split between the US allies, more severe than in 2004 when Saudi Arabia, Bahrain and the UAE withdrew their ambassadors from Doha.
Mahjoob Zweiri is an associate professor in contemporary Middle East history at Qatar University.
He says the decision appears to have been fast-tracked by a series of recent events.
Among them are leaked emails apparently from the UAE ambassador to the United States that appear to suggest his collusion with a pro-Israeli group against Qatar.
Majoob Zweri says he believes US president Donald Trump's increased engagement with Gulf states may have been a catalyst, too.
"The visit of (the UAE's Sheikh) Mohammed bin Zayed to Trump just the days before Trump's visit to Riyadh did indicate that there's something going on in terms of coordination between Washington and Abu Dhabi. And there was sort of information about why this visit just happened days before the other meeting would take place in Riyadh. I think there was, sort of, an expectation."
Mahjoob Zweiri says there is also the question of Qatar's perceived relationship with Iran, Saudi Arabia's arch rival, amid a renewed US push against Iran.
But in Canberra, Professor Amin Saikal at the Australian National University says the move weakens the GCC.
"They are predominantly Arab and Sunni states, and this could really undermine the Gulf Cooperation Council, which came into existence in the wake of, or shortly after, the Iranian revolution in 1978-79. And this means that, now, it is extremely difficult for the Gulf Cooperation Council to operate as a very cooperative body."
