Eight British personnel from 3 Commando Brigade Royal Marines are reported to have died when an American helicopter crashed in northern Kuwait last night.

The veteran CH-46 Sea Knight helicopter, used by the US Marine Corps, was said to have been undertaking a routine transfer of British personnel when it came down not far from the Iraqi border. Iraqi claims that they had shot down the aircraft have been denied by Allied sources.

The deaths are the first British casualties of the war, while the four-strong American helicopter flight crew are also believed to have died.

Accident investigators are already at the crash site, and Defence Secretary Geoff Hoon said that it was a priority to identify the victims and inform their next of kin as soon as possible.

Troops from 40 Commando Royal Marines have been involved in an amphibious assault on the Al-Faw peninsula – the narrow strip of coastline which gives Iraq access to the Gulf.

The area is of prime strategic importance to post-war plans, as oil produced in the region is piped to the peninsula through manifolds which feed offshore installations, providing a vital source of revenue for the country.

This revenue forms a key plank in the rebuilding strategy after the military phase of the campaign to remove Saddam Hussein.

In the last Gulf War in the early 1990s oil wells in the area were set alight and the manifolds sabotaged, pouring crude oil into the Gulf and causing massive pollution in the region, and an early objective of the assault on the peninsula was to ensure similar damage was not caused.

Early indications are that the mission, in which 40 Commando were heavily involved, was accomplished with no British casualties and little environmental damage.

There are now unconfirmed reports that the nearby town on Um-Kasr, which includes an Iraqi naval base, is said to be under assault from Allied forces.

The Commanding Officer of 40 Commando, Lt Col Gordon Messenger, also said that upward of 60 prisoners of war have been taken as his men faced light resistance on the peninsula.

Journalists with Allied forces are now reporting that there is a major armoured push to the north, although military commanders will not say what their next objectives are to prevent the Iraqis marshalling their defences.

The main land assault, backed by missiles and artillery, began yesterday, and the Ministry of Defence has confirmed that British submarine-launched Tomahawk Land Attack Missiles (TLAMs) were fired at Iraqi targets last night.

Ships of the Royal Navy’s Amphibious Task Group in the Northern Arabian Gulf were used as one of the platforms for the air and sea assault on the Al-Faw peninsula – other elements of 40 Commando were flown in by helicopter from Kuwait – and the MOD also confirmed that the assault was backed by naval gunfire support from Royal Navy ships.

MOD sources would not, however, confirm reports that British TLAM cruise missiles were fired at Baghdad on the opening night of the campaign.

The Queen has sent a message of support to the Armed Forces and civilian personnel in the Gulf, expressing her pride in them and her confidence in their professionalism and commitment.

And Prime Minister Tony Blair broadcast a message to the nation on television last night, in which he confirmed that the objectives are to “remove Saddam Hussein from power, and disarm Iraq of its weapons of mass destruction”.

He also acknowledged that “this course of action has produced deep divisions of opinion in our country. But I know also the British people will now be united in sending our Armed Forces our thoughts and prayers.

“They are the finest in the world and their families and all of Britain can have great pride in them.”

And in a statement to the House of Commons yesterday, Defence Secretary Geoff Hoon outlined the current state of the situation in the Gulf, itemising the British contribution: a naval force of 29 RN and RFA ships; a land force led by HQ 1(UK) Armoured Division and including 3 Commando Brigade RM, 16 Air Assault Brigade, 7th Armoured Brigade and 102 Logistics Brigade, and an air force of around 100 fixed wing aircraft and 27 helicopters – a total of some 45,000 Servicemen and women.