Saudi Arabia, Egypt, Bahrain and the United Arab Emirates have cut diplomatic ties with Qatar, accusing it of bringing instability in the region.
The countries say Qatar is supporting terrorist groups including the Muslim Brotherhood.
The Saudi state news agency SPA said Riyadh had closed its borders, severing land, sea and air contact.
It cited officials as saying it was to "protect its national security from the dangers of terrorism and extremism".
Egypt has also closed its airspace and ports for all Qatari transportation.
