Kabul ? A roadside bomb killed four American troops in southern Afghanistan, the U.S. said Friday, as a U.N.-backed panel finished most of its investigation into whether the level of fraud in the August presidential election would force a runoff.

Rising U.S. casualties and the political crisis triggered by a fraud-marred election have prompted the Obama administration to review its entire Afghanistan war strategy, including proposals to send thousands more troops here or shift the focus to missile strikes and special operations raid against al-Qaida figures in Pakistan.

The deaths bring to 25 the number of American service members killed in Afghanistan this month, according to an Associated Press count.