Barack Obama has rejected suggestions that the war in Afghanistan is becoming a repeat of the conflict in Vietnam more than three decades ago.
In his speech on Tuesday at the West Point military academy, the US president said any comparison between the two wars was based on "a false reading of history".
The speech was intended to redefine US goals in Afghanistan, bolster public support for US involvement, and set out a plan leading for eventual withdrawal of American troops.
The spectre of "another Vietnam" has long hung over the eight-year-old Afghan war, with critics saying an increase in troops simply places the US at risk of being sucked into repeat of a Vietnam-style "quagmire".
That war, which began in the early 1960s and ended with the fall of South Vietnam in 1975, saw ever larger numbers of US forces deployed and doomed the presidency of Lyndon Johnson.
The conflict was the deadliest for US forces since the Second World War, killing more than 58,000 US troops, at least 60 times more than have so far died in Afghanistan.
|The US humiliation in Vietnam continues to carry a bitter political legacy [AP]
At its height in 1968 the US had some 549,000 troops deployed in Vietnam, about eight times more than are currently in Afghanistan.
But despite those differences, the American humiliation in Vietnam carries a bitter political legacy and has frequently been used by critics of US involvement in Afghanistan who say the war is unwinnable.
Critics of the Afghan war have pointed to what they say are other similarities.
As with Vietnam the US is undoubtedly the superior military force and wins every fight it gets into, but ultimately makes little progress in winning the war.
In addition, critics argue that like Vietnam the US presence in Afghanistan is propping up a corrupt and ineffectual government that lacks popular support.
Presidential elections in Afghanistan earlier this year, which eventually saw Hamid Karzai returned to power, were beset by widespread fraud and allegation.
But in his West Point speech on Tuesday Obama hit back at those calling for the US to cut its losses and pull out of Afghanistan.
Unlike in Vietnam, he said, the US has been joined by a coalition of 43 nations in Afghanistan and was not facing a broad-based popular insurgency.
But he said the most important difference with Vietnam was that "the American people were viciously attacked from Afghanistan" adding that they remain "a target for those same extremists who are plotting along its border".