KANDAHAR, Afghanistan - A roadside bomb struck a U.S. convoy in southern Afghanistan on Tuesday, killing three American troops, while a motorcycle bomb in a crowded village market killed at least three Afghan civilians, officials said.

A NATO spokesman, Col. Thomas Collins, said the blast hit the American convoy in the Zhari district of Kandahar province, the spiritual heartland of the Taliban and one of the most volatile regions in Afghanistan.

Collins originally said four U.S. troops were killed, but Capt. Luca Carniel later said NATO had revised the death toll to three.

The attack follows a truck bombing a day earlier on a NATO outpost in Helmand province that killed three soldiers from the former Soviet republic of Georgia. So far this year, 58 international service troops have been killed in Afghanistan, according to an Associated Press count. Of that tally, 44 were U.S. service members.

Earlier Tuesday, a bomb hidden in a parked motorcycle ripped through a packed market in the village of Safar in Helmand, according to Omer Zawak, a spokesman for the provincial governor. Three people were killed, he said.

Also Tuesday, the Taliban released the last four of eight Turks taken hostage last month.

In an e-mail statement, Taliban spokesman Zabiullah Mujahed said the group freed the four Tuesday as a "goodwill" gesture to fellow Muslims. Turkey's president Recep Tayyip Erdogan confirmed their release.

The eight Turks, along with an Afghan translator and two pilots, were captured after bad weather forced their helicopter to make an emergency landing in eastern Afghanistan on April 21.

Mujahed did not make reference to the fate of the Afghan translator and two pilots.