US President George W Bush has paid tribute to two servicemen who have died in a helicopter accident in Pakistan.
A defence official said the aircraft crashed while it was on search-and-rescue duty for commandos who were raiding Taliban positions in Afghanistan.
Mr Bush, after meeting Japanese Prime Minister Junichiro Koizumi at an economic summit in Shanghai, China, said he grieved for the soldiers and their families.
"The important thing for me to tell the American people is these soldiers will not have died in vain," the president said.
"It is hard to express my gratitude ... two people who are willing to sacrifice for freedom.
"The nation feels the same gratitude. The soldiers died in a cause that is just and right, and we will prevail."
The US president said Americans were prepared for the casualties that come with war. "They understand there will be sacrifices," he said.
Mr Bush refused to confirm US forces were in Afghanistan, but he said: "Let me reiterate what I've told the American people and the world. We will use whatever means are necessary to achieve our objective."
Mr Bush said of the US operation in general: "I am satisfied we are making very good progress.
PA