McChrystal's dismissal came after publication of an article in Rolling Stone, The Runaway General, which portrayed him and his inner circle as being out of control, and making contemptuous and dismissive remarks about the US civilian leadership.

It also included a colourful account of a boisterous party in an Irish bar in Paris.

The investigation expressed doubts about the version of some events reported in the article, written by Michael Hastings, who spent several days with McChrystal and his team. The investigation added that it could not substantiate some of the quotes.

The investigation, carried out by the Pentagon's office of inspector general, concluded: "The evidence was insufficient to substantiate a violation of applicable department of defense standards with respect to any of the incidents on which we focused. Not all of the events at issue occurred as reported in the article.

"In some instances, we found no witness who acknowledged making or hearing the comments as reported. In other instances, we confirmed that the general substance of an incident at issue occurred, but not in the exact context described in the article."

The article, published in June last year, suggested that McChrystal was unimpressed with Obama at their first meeting, and that one of his team viewed the White House national security adviser, James Jones, as a clown. His team was also alleged to have been dismissive of vice-president Joe Biden and the late state department envoy to Afghanistan and Pakistan, Richard Holbrooke.

At the time, McChrystal apologised after the piece, saying it was a mistake reflecting poor judgment and should never have happened. He flew back to Washington to see Obama, who dismissed him, saying: "The conduct represented in the recently published article does not meet the standard that should be set by a commanding general."

The investigation's conclusions open Obama to charges that he was too hasty in dismissing McChrystal.

The former general, though no longer in the army, was partially rehabilitated last week when the White House invited him to join a panel to try to improve the life of military families.

The new investigation is more favourable to McChrystal than an initial one published in August last year.

There was no immediate response from either McChrystal or Hastings to the new findings.

On some of the specifics, the investigation found no evidence that McChrystal made a middle finger gesture to another officer and concluded that, even if he had, this did not constitute a violation of standards.

Dealing with another alleged comment, the investigation's report said: "Witness testimony led us to conclude that the comment made by a staff member that a dinner event was 'fucking gay', or words to that effect, was made, but we could not identify the speaker. Witnesses testified that the comment was not directed toward any French official, or toward the French government or military."

No evidence was found that McChrystal said that he was disappointed with Obama on first meeting him. With regard to the behaviour of him and his staff at the Irish bar in Paris, Kitty O'Shea's, the report said: "Our analysis of witness testimony led us to conclude that the behaviour of General McChrystal and his staff at Kitty O'Shea's, while celebratory, was not drunken, disorderly, disgraceful, or offensive. Their conduct did not violate any department of defense standards."

It found no evidence that one of McChrystal's team had called the White House national security adviser a clown.