The Taliban claimed responsibility for the blast, which came a day after the U.S. death toll in the war in Afghanistan reached 2,000 troops and as relations between international forces and their Afghan partners have been pushed to the breaking point by a surge in insider attacks by Afghan allies.
The bomber struck a group of Afghan police and international troops shortly after they got out of their vehicles to walk through a market area in Khost city, the capital of Khost province, said provincial government spokesman Baryalai Wakman.
Six civilians and four police officers were killed in the blast, Wakman said. He said the police officers were part of a specialized quick-reaction force.
Blood could be seen on the market road as Afghan police and soldiers tried to clean up the area after the blast. Slippers and bicycle parts were strewn about.
"I heard the explosion and came right to this area. I saw the dead bodies of policemen and of civilians right here," said policeman Hashmat Khan, who ran to the site of the blast from his job as security for a nearby bank.
Coalition spokesman Maj. Adam Wojack would only confirm that three NATO service members and their translator died in a bombing in the east on Monday, without giving an exact location or the nationalities of the dead.
The international military alliance usually waits for individual nations to announce details on deaths. Most of the troops in the east and in Khost province are American. It was not immediately clear if the translator was an Afghan citizen or a foreigner, Wojack said.
Dozens of Afghan civilians were also wounded in the bombing. The city's hospital alone was treating about 30 people injured in the explosion, said Dr. Amir Pacha, a physician working there. He added there could be other victims being treated at nearby private clinics.
Taliban spokesman Zabiullah Mujahid said in text messages to media that the insurgent group was behind the attack.
Joint patrols between NATO and Afghan forces have become more limited following a tide of attacks by Afghan soldiers and police on their international allies. Last month, the U.S. military issued new orders that require units to get approval from higher-ups before conducting operations with Afghans. Then, two weeks later, U.S. officials said most missions were being conducted with Afghans again, though the system of approvals has remained in place.
The close contact -- coalition forces working side by side with Afghan troops as advisers, mentors and trainers -- is a key part of the U.S. strategy for putting the Afghans in the lead as the U.S. and other nations prepare to pull out their last combat troops by the end of 2014.
But the rising death toll for international troops has increased calls in the U.S. and other allies to get out as soon as possible. On Sunday, a U.S. official confirmed that an American soldier was killed in a firefight that broke out between Afghan and U.S. troops, sparked by either a premeditated attack or confusion about the origins of an insurgent strike.
According to an Associated Press count, that soldier's death brought American troop deaths in Afghanistan since the 2001 invasion to 2,000 -- a cold reminder of the perils that remain after an 11-year conflict.