Former Soviet leader Mikhail Gorbachev, who withdrew troops from Afghanistan in 1989 after a 10-year war, says the United States has no option but to withdraw its own forces.
"Victory is impossible in Afghanistan," Gorbachev told BBC's Moscow correspondent. "Obama is right to pull the troops out. No matter how difficult it will be."
President Barack Obama has said he is committed to begin withdrawing US forces from Afghanistan in July of 2011.
In August, General James Conway criticized the president's deadline, saying it "probably giving our enemy sustenance."
"I honestly think it will be a few years before conditions on the ground are such that turnover will be possible for us," Conway added.
Perhaps due to the criticism of General Conway and others, Vice President Joe Biden claimed the deadline was not an "end date," but rather when Afghanistan would begin exercising more sovereignty.
"Everybody says, 'Is that an end date?' It is not," Biden said in a speech. "We are not leaving in 2011. We are beginning the transition."
"What's the alternative - another Vietnam?" continued Gorbachev. "Sending in half-a-million troops? That wouldn't work."
Before the Soviet Union withdrew its forces from Afghanistan, Gorbachev claims the US, Iran, India, and Pakistan agreed that Afghanistan should remain neutral.
"We had hoped America would abide by the agreement that we reached that Afghanistan should be a neutral, democratic country, that would have good relations with its neighbors and with both the US and the USSR," said Gorbachev.
"The Americans always said they supported this, but at the same time they were training militants - the same ones who today are terrorizing Afghanistan and more and more of Pakistan," he added.
Gorbachev's statements echo those recently made by senior US intelligence officials.
"The insurgency seems to be maintaining its resilience," a senior Defense Department official told the Washington Post.
"For senior leadership, not much has changed. At most we are seeing lines of support disrupted, but it's temporary."
Gorbachev's comments came amid news that Dmitry Medvedev, the Russian president, will attend a NATO summit next month in Lisbon to announce his country's return to the war in Afghanistan.
Russia is expected to supply NATO with several dozen helicopters and train the Afghan army and counter-narcotics troops, The Independent reports.