British submarines have launched cruise missiles at Afghanistan as part of the attacks against the Taleban and Osama bin Laden.Prime Minister Tony Blair said the military base at Diego Garcia, missile-firing submarines and reconaissance aircraft were involved in the attacks.
He said the submarines, which carry cruise missiles, had been used on Sunday night, and the aircraft would be used in coming days.
The decision had not been taken lightly, and that the start of action was a "moment of utmost gravity for the world," he said in a statement at 10 Downing Street.
"But we know that sometimes to safeguard peace we have to fight," he said.
Mr Blair said it was very important that Britain be involved, as the 11 September terrorist attacks were the worst against UK citizens in history.
"This atrocity was an attack on us all, on people of all faiths and people of none," he said.
He praised the global coalition which had been built up in response to the attacks and said the al-Queda network threatened any nation which did not share its fanatical views.
'Immense anxiety'
He reiterated that this was not a war with Islam.
Mr Blair paid tribute to the UK armed forces, saying he knew they were "amongst the very best in the world".
But he said he understood they were carrying an "immense burden" and would be feeling "immense anxiety" - as would the British people.
He said he knew there were dangers in action, but said the dangers of inaction were "far, far worse".
"Britain has learnt that before in its history. We only act when the cause is just and in this case it is just.
"We will not let up or rest until our objectives are met in full."
Mr Blair said there was no doubt in his mind that the US terrorist attacks had been carried out by Osama Bin Laden and his al-Queda terrorist network.
He added that it was also clear that the Taleban authorities in Afghanistan were sheltering him.
"They were given the choice of siding with justice and siding with terror, and they chose to side with terror," he said.
He said action was being taken on military, diplomatic and humanitarian fronts.
And he said the military plan had been put together to avoid as far as was possible civilian casualties.
US President George W Bush had earlier confirmed UK involvement as he said in a White House address that the US had begun military action in response to the 11 September terrorist attacks.
"We are joined in this operation by our staunch friend, Great Britain," he said.
On Sunday evening there were reports of loud explosions and anti-aircraft fire in the Afghan capital Kabul and the city of Kandahar, the main stronghold of the ruling Taleban.
Explosions in Afghanistan
There were also reports of explosions in the eastern city of Jalalabad.
About 24 British Royal Navy warships - led by flagship aircraft carrier HMS Illustrious - and approximately 23,000 British troops are in the region.
They had been sent there before the 11 September US attacks for long-planned exercises with the Oman military, known as Saif Sareea 2.
Britain has previously said these forces would be available to take part in any military action against Osama Bin Laden or the Taleban.
The leader of the UK opposition Conservative party, Iain Duncan Smith, said he supported the action.
It sent the Taleban a strong message that if they refuse to hand over Bin Laden they would suffer the consequences, he said.
Parliament should be recalled at the "earliest possible opportunity" in the wake of the war, he said.