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.
The coalition blames the rise in troop deaths partly on the influx of reinforcements, which is allowing commanders to target previously untouched insurgent safe havens where rebels are mounting stiff resistance.
Gen David Petraeus, senior US and Nato commander in the country, warned last week fighting would "get harder before it gets easier".
In two of the most deadly recent incidents, three Americans died in eastern Afghanistan on one bomb attack on Tuesday. Five died in a single bomb attack in the south on Monday.
Military spokesmen would not say if the bombs hit vehicles or foot patrols.
Homemade bombs using old shells or homemade explosives and hidden in roads, tracks, walls, streams and buildings have become the Taliban's favoured weapon.
Their use has sparked an arms race with foreign troops evolving tactics, or relying on more heavily armed vehicles and mine detectors to try and avoid them.