The Arab world's biggest powers cut ties with Qatar today over alleged support for Islamists and Iran.
Saudi Arabia, Egypt, United Arab Emirates and Bahrain severed diplomatic relations with Qatar in a coordinated move.
Yemen, Libya's eastern-based government and the Maldives joined later.
Transport links shut down, triggering supply shortages.
Qatar, a small peninsular nation of 2.5 million people, denounced the action as predicated on lies about it supporting militants.
It has often been accused of being a funding source for Islamists, as has Saudi Arabia.
Iran, long at odds with Saudi Arabia and a behind-the-scenes target of the move, blamed US President Donald Trump's visit last month to the Saudi capital Riyadh and called for the sides to overcome their differences.
"What is happening is the preliminary result of the sword dance," tweeted Hamid Aboutalebi, deputy chief of staff to Iranian President Hassan Rouhani, referring to Mr Trump joining in a traditional dance with the Saudi king at the meeting.
Closing all transport links with Qatar, the three Gulf states gave Qatari visitors and residents two weeks to leave, and Saudi Arabia, Bahrain and Egypt banned Qatari planes from landing and forbade them from crossing their air space.
The UAE and Saudi Arabia stopped exports of white sugar to Qatar, a potential hit to consumers during the holy month of Ramadan, when demand is high.
Some residents in Qatar began stockpiling food and supplies, an expatriate said.
Supply difficulties quickly developed. Two Middle East trade sources spoke of thousands of trucks carrying food stuck at the Saudi border, unable make the sole overland frontier crossing into Qatar.
About 80% of Qatar's food requirements are sourced via bigger Gulf Arab neighbours. Trade sources pointed to the likelihood of shortages growing in Qatar until the crisis eased.
Along with Egypt, however, the UAE and Saudi Arabia could be vulnerable to retaliation, being highly dependent on Qatar for liquefied natural gas.
The United States called for a resolution of the dispute soon, saying its partnerships with Gulf nations were vital.
"All of our partnerships in the Gulf are incredibly important and we count on the parties to find a way to resolve their differences sooner rather than later," a State Department official said.
The US military said it had seen no impact to its Gulf-area operations, intended mainly as a bulwark against Iran, and added that it was grateful for Qatar's longstanding support of a US presence and commitment to regional security.
The diplomatic bust-up threatens the international prestige of Qatar, which has a large US military base and is set to host the 2022 soccer World Cup.
Soccer's governing body FIFA said it was in "regular contact" with Qatar's 2022 organising committee but did not comment directly on the diplomatic situation.
The aggressive tone Mr Trump brought in his visit to over 50 Muslim leaders in Riyadh on Iran and on terrorism is seen as having laid the groundwork for the diplomatic crisis.
Qatar's backing of Islamists dates to a decision by the current emir's father to end a tradition of automatic deference to Saudi Arabia, the dominant Gulf Arab power, and forge the widest possible array of allies.
Qatar subsequently cultivated not only Islamists like US foes Iran, Hamas and the Taliban in pursuit of leverage, but also the US itself, hosting the largest US air base in the Middle East.
Qatar has for years presented itself as a mediator and powerbroker for the region's many disputes.
But Egypt and the Gulf Arab states resent Qatar's support for Islamists, especially the Muslim Brotherhood, which they see as a political enemy.
Muslim Brotherhood groups allied to Qatar are now mostly on the backfoot in the region, especially after a 2013 military takeover in Egypt ousted the elected Islamist president.
The ex-army chief and now president, Abdel Fattah al-Sisi, along with Egypt’s allies in Saudi Arabia and the UAE, blacklist the Brotherhood as a terrorist organisation.
The Brotherhood denies this, saying it supports only peaceful politics.
Saudi Arabia accused Qatar on Monday of backing militant groups and broadcasting their ideology, an apparent reference to Qatar's influential state-owned satellite channel al-Jazeera.
Later in the day, the kingdom shut the Saudi bureau of 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," Saudi state news agency SPA said.
Al Jazeera says it is an independent news service giving a voice to everyone in the region.
Saudi Arabia also accused Qatar of supporting what it described as Iranian-backed militants in the restive, largely Shia Muslim-populated eastern Saudi region of Qatif, as well as in Bahrain.
Qatar was also expelled from the Saudi-led coalition fighting a war in Yemen.
The state news agency in Egypt said Qatari 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".
Qatar denied it was interfering in the affairs of others.
"The campaign of incitement is based on lies that had reached the level of complete fabrications," the Qatari foreign ministry said in a statement.
Turkey also called for dialogue to settle the dispute and a government spokesman said President Tayyip Erdogan was working for a diplomatic solution to the rift.
Sudan expressed its concern over the row and offered to mediate between all sides.
