Gulf troops intervene in Bahrain against pro-democracy protesters

Television footage showed convoys of unmarked, armoured vehicles crossing from Saudi’s Eastern Province into Bahrain, prompting the alarm of the United Nations and the United States.

Saudi’s Eastern Province is house to the US Fifth Fleet.

The Saudi government said it had responded to a call for help from its neighbour: "The council of ministers has confirmed that it has answered a request by Bahrain for support," the Saudi government said in a statement.

Under an agreement of the six-country Gulf Cooperation Council (GCC), "any harm done to the security of a member state is considered a harm done to the security of all members," it said.

The United Arab Emirates also said it had sent some 500 police to help "defuse tension".

The opposition alliance said any foreign force would be treated as an invading army.

"We consider the arrival of any soldier, or military vehicle, into Bahrain territory... an overt occupation of the kingdom of Bahrain and a conspiracy against the unarmed people of Bahrain," the opposition said in a statement.

But authorities called on the population to "cooperate fully and to welcome" the troops.

UN chief Ban Ki-moon’s spokesman said Ki-moon was "troubled" by the arrival of the forces: "He appeals to all concerned to exercise maximum restraint and to do everything possible to prevent the use of force and further violence."

Iran's foreign ministry spokesman said the military intervention in Bahrain by Gulf States is "unacceptable" and will complicate the already volatile situation there.

The White House also called on the Gulf forces to respect the rights of the people of Bahrain, whilst stating that a call for forces to be pulled out has been declined: “This is not an invasion of a country.”