A diplomatic row between Gulf countries has intensified, over accusations that Qatar are supporting terrorism.
Egypt, Saudi Arabia, Bahrain and the United Arab Emirates have all said they are cutting diplomatic ties with the nation, over the country's support for Islamist groups.
The Saudi government has said it is also closing its border with Qatar, saying it is to "protect its national security from extremism".
Saudi Arabia also said Qatari troops would be pulled from the ongoing war in Yemen.
The countries also said they would eject Qatar's diplomats from their territories.
Qatar's Foreign Affairs Ministry said there was "no legitimate justification" for the countries' decision, though it vowed its citizens would not be affected by the "violation of its sovereignty".
The four nations also said they planned to cut air and sea traffic to the peninsular country.
Bahrain blamed Qatar's "media incitement, support for armed terrorist activities and funding linked to Iranian groups to carry out sabotage and spreading chaos in Bahrain" for its decision.
The decision comes after Qatar claimed in late May that hackers took over the site of its state-run news agency and published what it called fake comments from its ruling emir about Iran and Israel.
Qatar is also home to the sprawling al-Udeid Air Base, which is home to the US military's Central Command and some 10,000 American troops.
It was not clear if the decision would affect American military operations.
Saudi Arabia said it took the decision to cut diplomatic ties due to Qatar's "embrace of various terrorist and sectarian groups aimed at destabilising the region" including the Muslim Brotherhood, al Qaida, the Islamic State group and groups supported by Iran in the kingdom's restive eastern province of Qatif.
Egypt's Foreign Ministry accused Qatar of taking an "antagonist approach" toward Egypt and said "all attempts to stop it from supporting terrorist groups failed".
The tiny island nation of Bahrain blamed Qatar's "media incitement, support for armed terrorist activities and funding linked to Iranian groups to carry out sabotage and spreading chaos in Bahrain" for its decision.
The US Navy's 5th Fleet, based in Bahrain, did not immediately respond to a request for comment about whether the decision would affect its operations.
US secretary of state Rex Tillerson said he did not believe the diplomatic crisis would affect the war against the Islamic State group in Iraq and Syria.
"I think what we're witnessing is a growing list of disbelief in the countries for some time, and they've bubbled up to take action in order to have those differences addressed," Mr Tillerson said.
"We certainly would encourage the parties to sit down together and address these differences."