One of the terminals would be built at the Petroplus site

Qatar in the Middle East, which has some of the world's largest natural gas reserves, will provide the gas for the sites in a 25-year deal.

Qatar Petroleum said the first shipment could arrive by late 2007.

Planning permission for the terminals has been granted despite protests over safety by local residents.

Two sites - the Petroplus plant at Waterston and the former Esso refinery at Milford Haven - have been approved by Pembrokeshire council.

Objectors had said the Petroplus plant should not be built so close to a town because they claimed there was not enough information about LNG to be certain it would not pose a risk to people living nearby.

They suggested the terminals could be sited off-shore instead.

Malaysian company Petronas plans to ship liquefied natural gas (LNG) - gas cooled down to liquid form to make it easier to transport - from all over the world.

It will then be fed into the UK gas supply in a deal worth a potential £4bn over 15 years.

The increase in traffic could see Milford Haven become the third busiest port in the UK.