(Adds Pentagon comments)
By Jonathon Burch
KABUL, Oct 6 (Reuters) - The war in Afghanistan cannot be won militarily and success is only possible through political means including dialogue between all relevant parties, the United Nations' top official in the country said on Monday.
His comments come after Britain's military commander in Afghanistan said the war could not be won and that the goal was to reduce the insurgency to a level where it was no longer a strategic threat and could be dealt with by the Afghan army.
Brigadier Mark Carleton-Smith said if the Taliban were willing to talk, that might be "precisely the sort of progress" needed to end the insurgency.
"I've always said to those that talk about the military surge ... what we need most of all is a political surge, more political energy," Kai Eide, the U.N. special envoy to Afghanistan, told a news conference in Kabul.
"We all know that we cannot win it militarily. It has to be won through political means. That means political engagement."
Eide said success depended on speaking with all sides in the conflict. "If you want to have relevant results, you must speak to those who are relevant. If you want to have results that matter, you must speak to those who matter," he said.
Pentagon spokesman Bryan Whitman said: "We're not losing in Afghanistan, though there certainly is a recognition that there's more we could be doing there."
Asked about the possibility of negotiations with the Taliban, he replied: "This is not an element of our strategy. They have terrorized Afghan society for years."
The British ambassador to Kabul said a troop surge would only create more targets for the Taliban. The comments were made to a French colleague who sent a telegram to Paris which was leaked and published in Le Canard Enchaine newspaper last week.
But the U.S. general commanding NATO forces said last month he needed three more brigades -- possibly around 15,000 troops -- on top of an extra 4,000 soldiers due to arrive in January.
Faced with the persistent reluctance of some of its European allies to send more troops to Afghanistan or allow them to fight once there, the United States has asked Japan and NATO countries to help foot the $17-billion bill to build up the Afghan army.
"The faster we get the (Afghan army) to the size and strength they need to be, the less they depend on us for providing security," said Pentagon press secretary Geoff Morrell.
The Afghan Defence Ministry says the cost of one foreign soldier in Afghanistan is equal to more than 60 Afghan troops.
More foreign troops have been killed in Afghanistan already this year than in any entire year since U.S.-led and Afghan forces toppled the Taliban after the Sept. 11 attacks in 2001.
As casualties mount, so have Western calls for negotiations with the militants to bring an end to the conflict.
But the Taliban have repeatedly rejected the idea of talks unless all 70,000 foreign troops leave the country.
"As we said before, as long as the invader forces are in Afghanistan, we won't participate in any negotiations," Taliban spokesman Qari Mohammad Yousuf told the Pakistan-based Afghan news agency, AIP, on Monday.
Yousuf also denied reports that negotiations had taken place between the Taliban and the Afghan government in Saudi Arabia.
"All these reports are wrong. We have neither held talks with any government bodies nor have we sent any delegation for talks anywhere," Yousuf told AIP.
Afghan President Hamid Karzai has also denied the reports but said he had asked the king of Saudi Arabia to help in talks with the militant group. Any negotiations would only take place in Afghanistan, he said.
Saudi Arabia was one of the few countries to recognise a Taliban government when they ruled most of Afghanistan in the 1990s. The hardline Islamists were ousted in late 2001. (Additional reporting by Kristin Roberts in Washington and David Ljunggren in Ottawa; Editing by Ralph Boulton)