Saudi Arabia, the United Arab Emirates, Egypt and Bahrain say they are severing diplomatic relations with Qatar.
The Saudi kingdom said it was cutting the ties to its neighbour and has pulled all Qatari troops from the ongoing war in Yemen.
The kingdom made the announcement via its state-run Saudi Press Agency early on Monday, saying it was taking the action for what it called the protection of national security.
The statement appeared to be timed in concert with an earlier announcement by Bahrain similarly cutting ties.
Qatar had no immediate comment.
The dispute between Qatar and the Gulf’s Arab countries escalated after a recent hack of Qatar’s state-run news agency. It has spiralled since.