Armoured troops rolled into Bahrain from neighbouring Saudi Arabia yesterday to help restore order in the strategic Gulf kingdom, where pro-democracy demonstrators have shut down the financial centre.

Thousands of mainly Shiite protesters occupied Manama’s business district, turning the regional banking hub into a ghost town as they pressed their calls for democratic change from the Sunni Muslim monarchy.

The Saudi government said it had responded to a call for help from its neighbour as Saudi-led forces from the Gulf countries’ joint Peninsula Shield Force crossed the causeway separating the two countries.

“The council of ministers has confirmed that it has answered a request by Bahrain for support,” the Saudi government said in a statement carried by the SPA state news agency.

It said that 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”.

The exact make-up of the force was not known, but the United Arab Emirates also confirmed it was participating in the operation. The GCC groups Bahrain, Kuwait, Oman, Qatar, Saudi Arabia and the UAE.

Television footage showed convoys of unmarked, desert-brown coloured armoured vehicles crossing the causeway from Saudi’s Eastern Province into Bahrain, the home of the US Fifth Fleet.

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