AMERICA is to spend £1billion on an embassy in Baghdad "more secure than the Pentagon".

Plans for the hi-tech complex are being kept secret because of the terrorist threat in Iraq.

The exact location is not being released until later this year but it is likely to be built in the heavily fortified Green Zone area where the Iraqi government and US military command is based.

The embassy will be guarded by 15ft blast walls and ground-to-air missiles and the main building will have bunkers for use during air offensives.

The grounds will include as many as 300 houses for consular and military officials.

And a large-scale barracks will be built for Marines who will protect what will be Washington's biggest and most secure overseas building.

A US source in the Middle East said last night: "Plans for the embassy building are being kept behind closed doors because of the terrorist threat.

"It will be more secure than The Pentagon because it will be under constant threat from attack." The Green Zone is the safest part of Baghdad, surrounded by concrete blast walls and checkpoints.

The US also wants to build four massive military superbases around Iraq's capital.

The plans will fuel speculation they want to keep a firm foothold in Iraq for many years.

An Iraqi security source said last night: "The plans for the embassy building will make it the largest and best protected diplomatic building overseas for the US.

"You may as well move the Pentagon to Iraq. It will be amazingly secure but it also flies in the face of claims American is preparing to leave Iraq to be policed and governed by Iraqis.

"Plans for four superbases across the country will only reinforce the view that the US is here to stay for the duration."

The move comes despite Donald Rumsfeld revealing last week that US troop numbers in Iraq are to be reduced by 7,000 to 153,000.

Tony Blair has also predicted British troops could start pulling out this May.

Backing among the American public for President Bush's action in Iraq has fallen. Despite the opposition a Kuwait-based construction company has already been handed £175million ($300 million) of the building deal.

Plans for four huge military bases placed strategically around Baghdad are also being drawn up.

The superbases will be in central Iraq, close to the capital, and also to the north, west and east of Baghdad.

Several other Middle Eastern and American building firms are tendering for the remaining budget.

Funding will probably come from Iraqi oil revenues channelled into redeveloping the country.

America has a string of 'secret' military bases throughout the Gulf states, including Kuwait, Bahrain and Qatar.

The huge desert complexes, including airstrips and aircraft hangars, are up to 20 miles square and are not featured on civilian maps.

They started to appear after the first Gulf War 15 years ago, infuriating Islamic extremists and the al-Qaeda terror network.