Six American troops were killed in a roadside blast today in eastern Afghanistan, a U.S. official told ABC News. Details about the deadly incident remain vague.

Earlier today, a press release by NATO's International Security Assistance Force said six ISAF servicemembers "died following an improvised explosive device attack in eastern Afghanistan today."

The nationalities of the victims were not identified because "it is ISAF policy to defer casualty identification procedures to the relevant national authorities," the statement said.

A U.S. official confirmed to ABC News that the six killed in today's attack were Americans, but did not have specific details about the incident.

Roadside bombings have been the main cause of casualties for U.S. troops fighting in Afghanistan, but Afghan civilians have also suffered at the hands of IEDs.

Two roadside bombs went off earlier today in Kandahar Province, killing at least 14 civilians, including women and children.

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Most of the roadside bombs used in Afghanistan are made with the fertilizer ammonium nitrate. Efforts to reduce the smuggling of that fertilizer from Pakistan have proven mixed.

Top military leaders have said that eastern Afghanistan will be the focus of security efforts over the next two years as NATO troops prepare to leave by the end of 2014.

Most of the NATO troops operating in eastern Afghanistan are American.

By the middle of next year, Afghan Security Forces will be in the lead for security throughout Afghanistan, with U.S. troops in a combat support role.