Saudi Arabia, the United Arab Emirates (UAE) and Bahrain said on Wednesday they were withdrawing their ambassadors from Qatar because Doha had not implemented an agreement among Gulf countries not to interfere in each others' internal affairs.

The move, conveyed in a joint statement by the three countries, is unprecedented in the three-decade history of the Gulf Cooperation Council, an alliance of Saudi Arabia, Bahrain, Kuwait, Qatar, UAE and Oman.

Qatar has been a maverick in the region, backing Islamist groups in Egypt, Syria and elsewhere in the Middle East that are viewed with suspicion or outright hostility by some fellow GCC members.

The statement said GCC members had signed an agreement on November 23 not to back "anyone threatening the security and stability of the GCC whether as groups or individuals - via direct security work or through political influence, and not to support hostile media".

GCC foreign ministers had met in Riyadh on Tuesday to try to persuade Qatar to implement the agreement, it said.

"But unfortunately, these efforts did not result in Qatar's agreement to abide by these measures, which prompted the three countries to start what they saw as necessary, to protect their security and stability, by withdrawing their ambassadors from Qatar starting from today, March 5 2014," the statement said.

Qatar's foreign ministry said it would respond later.

A source close to the Saudi government said pressure on Qatar would continue until it made tangible steps to change its policies. "They have to divert their position on many issues and we are waiting for real signs of this, not just talk."

A Gulf diplomatic source said: "We expect Qatar to react to what just happened and withdraw from the policies and ideas that have isolated it as a country. As people we are very brotherly to one another and we don't want things to escalate."

Qatar's stock market tumbled 3 per cent after the decision. Other Gulf stock markets also dropped by much smaller margins.

There is significant cross-border investment in the stock markets of GCC countries by investors from other GCC nations. Saudi investors play a major role in all GCC markets. - Reuters