A senior US diplomat who resigned over the war in Afghanistan has told the BBC that the troop surge there "will not make a difference".
Matthew Hoh stepped down from his position in the US state department in October 2009.
The former marine, who served in Iraq, had previously been the senior US civilian official in Zabul province.
He told BBC Radio 4 that a political solution was needed to what he called a "35-year-old civil war".
Matthew Hoh's resignation was described by one leading American newspaper as having sent "ripples all the way to the White House".
In a letter sent to explain his decision, he wrote that he had lost understanding of and confidence in the strategic purposes of the United States' presence in Afghanistan.
'Faulty strategy'
In his first British interview since leaving his job, Mr Hoh has deepened that criticism with a strong attack on the increase in forces announced by President Obama.
"The 30,000 troops are not going to make a difference because of the vast size of Afghanistan, the difficulties of operating in that kind of terrain," he told BBC Radio 4's The World At One.
The extra forces will bring the total US troop strength to 100,000 - but that is still well short of the number Mr Hoh believes is needed to be effective in Afghanistan.
He said: "You'd need so many more thousands and thousands of troops. I think you'd probably need in the order of 400-500,000 troops to subjugate those rural parts of the country."
Mr Hoh went on to attack current Western strategy as "faulty", saying it was built on supporting an "corrupt" and "illegitimate" Afghan government.
Mr Hoh said that only a political solution, which brought in currently excluded members of Afghan society, would bring the stability which would lead to security.
"This is basically a 35-year-old civil war," he said.
"In 2001, when the west invaded and removed the Taliban, we put in place the Northern Alliance - basically putting in place the other side in that civil war.
"We did nothing to settle or resolve those political differences which have been going on in that country since the mid-70s.
"We need to find a political settlement in Afghanistan and unfortunately I don't think the present strategy of the West is going to lead to any kind of settlement which is going to end this civil war."
The full interview with Matthew Hoh is available via the World At One website