Twenty-one American troops have been killed in Afghanistan since Friday in one of the bloodiest periods of the summer.
A series of bomb attacks have badly hit US troops in eastern and southern Afghanistan in the past 48 hours.
The death toll among in the Nato-led coalition has reached 484 this year and is predicted to far surpass 2009’s total of 521.
Deaths have risen consistently each year since 2001. Afghan police and civilians have suffered far higher casualties.