Saudi Arabia, UAE, Bahrain and Egypt have cut diplomatic ties and all land sea and air contacts with Qatar, accusing the Persian Gulf country of supporting terrorism and interfering in their internal affairs.
Riyadh took the lead on Monday to sever relations and other countries fell in line after an official source said the kingdom "urges all brotherly countries and companies to do the same."
The kingdom said it made the decision, "proceeding from the exercise of its sovereign right guaranteed by international law and the protection of national security from the dangers of terrorism and extremism."
The United Arab Emirates gave Qatari diplomats 48 hours to leave the country, citing their "support, funding and embrace of terrorist, extremist and sectarian organizations," state news agency WAM reported.
Bahrain news agency said the tiny kingdom was cutting ties with Doha over its insistence on "shaking the security and stability of Bahrain and meddling in its affairs."
Egypt accused the Persian Gulf Arab state of supporting "terrorist" organizations, including the Muslim Brotherhood.
Tensions have escalated between Riyadh and Doha since an article appeared on Qatar's state-run news agency late in May, quoting the emir as criticizing the United States, Saudi Arabia, and their client states for attempting to stir up tensions with "Islamic power" Iran.
"Iran represents a regional and Islamic power that cannot be ignored and it is unwise to face up against it," the emir was quoted as saying. "It is a big power in the stabilization of the region."
The crisis follows US President Donald Trump's visit to the region last month, marked by the signing of a record $110-billion arms deal with Saudi Arabia.
US Secretary of State Rex Tillerson said the visit was aimed at getting Saudi Arabia and other Arab nations in the region to stand in "unity" with Israel and confront Iran.