A feud that has been simmering for years, blasted open as four Arab nations severed diplomatic relations with Qatar.
They moved swiftly to isolate the small but influential country after accusing Qatar's rulers of supporting terrorist factions and stoking regional conflicts.
The four countries - Saudi Arabia, the United Arab Emirates, Egypt and Bahrain - released separate and apparently coordinated statements saying they would cut air, sea and land links with Qatar, which hosts a forward base for the US military's Central Command and is home to the widely watched Al Jazeera network.
The feud - the most serious in decades among some the region's most key Western allies - has been in the background as Qatar increasingly flexed its political muscle across the region, including backing for the Muslim Brotherhood.
The diplomatic break came just weeks after US President Donald Trump met Arab and Muslim leaders in Saudi Arabia and called for a unified front against extremism and regional influence by rival Iran.
The visit was hailed by the Trump Administration as a success, but analysts in the region said at the time that it seemed likely to aggravate local disputes.
Trump's trip, they said, amounted to a us endorsement of the Saudi-led bloc that has increasingly demanded that other Arab states - including Qatar - fall in line with its positions, including a hard line against Iran and opposition to transnational Islamist groups.
The Brotherhood and affiliated groups, which favour Islamist-inspired policies, are seen by many Arab leaders as threat and have faced sharp crackdowns around the region since being ousted from power in Egypt in 2013.
The result was unusually bitter feud between Gulf monarchies that have long boasted in public of their "brotherly" relations, while competing behind the scenes for influence in a region riven by uprisings and wars, and haunted by resurgent militant groups.
The internationally recognised government of Yemen also broke ties with Qatar, Saudi news media reported. The stance appeared largely symbolic, however. The Yemeni Government of President Abed Rabbo Mansour Hadi, which is backed by Saudi Arabia, operates largely in exile because of the country's civil war and enjoys dwindling support in Yemen itself.
US Secretary of State Rex Tillerson and Defence Secretary Jim Mattis, travelling in Australia yesterday, asserted that the developments would not affect the US-led coalition fighting Sunni extremist groups in the Middle East.
"What we're witnessing is a growing list of irritants in the region that have been there for some time," he said.
Other nations with strategic ties in the region quickly urged for efforts to keep the diplomatic spat from widening.
"We see the stability in the Gulf region as our own unity and solidarity," Turkey's Foreign Minister Mevlut Cavusoglu told reporters in Ankara.
In Russia, a Kremlin statement said a "stable and peaceful" Gulf region was crucial to the region.
The United States uses bases in several of the countries to launch air operations against Isis (Islamic State). The US headquarters for the air war is located at the Al Udeid Air Base in Qatar.
For years, Qatar has drawn the ire of Arab neighbours for its support of the Muslim Brotherhood and affiliated Sunni Islamist groups, as well as for its sponsorship of the Al Jazeera television channel, which hosts frank discussions of politics in the region while also amplifying Qatar's pro-Islamist views.
Qatar is also among several Gulf countries, including Kuwait, Bahrain and Saudi Arabia, accused in recent years of looking the other way as its citizens privately sent money to Islamist militants abroad, including in Syria.
In response to Qatar's diplomatic isolation, the US Ambassador to Qatar, Dana Shell Smith, posted news releases on Twitter that were supportive of Qatar's efforts to combat terrorism financing. The US, one read, "supports Qatar's efforts to deny terrorist financiers access to its financial system".
The statements by the Arab countries, however, went beyond far beyond the usual criticism of Qatar for supporting Sunni extremists, accusing it of interference in conflicts from Yemen to the Sinai Peninsula.
The battery of charges included some that appeared implausible. Saudi Arabia, for instance, accused Qatar of supporting Yemen's Houthi rebels - even though Qatar has participated in a Saudi-led coalition fighting against the Houthis.
Bahrain, a stalwart ally of Saudi Arabia, accused Qatar of financing "groups associated with Iran to subvert and spread chaos in Bahrain".
Qatar's Foreign Ministry called the measures "unjustified" in a statement and said the decision to sever ties was a violation of the country's sovereignty, and "based on claims and allegations that have no basis in fact".
The first signs of the intensifying feud emerged soon after Trump's visit to Saudi Arabia. In the days that followed, the Saudi Government and its allies attacked Qatar for statements allegedly made by Qatar's emir that were sympathetic to Iran and militant groups like Hizbollah and Hamas.
Qatar later said the statements, which were posted on the state news agency, were fake and that the agency's website had been hacked. That explanation, however, did not stop the attacks on Qatar from media outlets loyal to the Saudi or Emirati governments.
Iran - a main regional rival of Saudi Arabia and its Gulf allies - linked Trump's visit to the harder line against Qatar.
"What is happening is the preliminary result of the sword dance," wrote Hamid Aboutalebi, a top aide to Iranian President Hassan Rouhani, in a tweet making reference to Trump's trip last month to Saudi Arabia and his participation in a traditional dance.
Later, Iran's Foreign Minister, Mohammad Javad Zarif, posted a Twitter message noting that the diplomatic spat broke out during the Islamic holy month of Ramadan, when Muslims are urged to avoid quarrels.
"Neighbours are permanent; geography can't be changed," Zarif wrote. "Coercion is never the solution. Dialog is imperative, especially during blessed Ramadan."
Oil prices rose on news of the diplomatic break. Qatar is a major supplier of liquefied natural gas and other gas-related products.
Qatar, a peninsula nation that shares its only land border with Saudi Arabia, was left facing potentially catastrophic isolation, as airlines in the UAE and Saudi Arabia announced they were halting flights, and as a local Qatari news outlet reported that residents there were flocking to supermarkets to stock up on food.