Kessler had described the first test results as "inexplicable"

The 28-year-old, who won the third stage of last year's Tour de France, was suspended on 27 June after testing positive for the hormone on 24 April.

But following the second positive result, the rider has been dismissed with immediate effect.

"This second piece of evidence condemns him for good," said a team statement.

Kessler joined Astana earlier this year, and recently finished fourth during the Fleche Wallonne race on 26 April.