A Russian-made grenade exploded in a crowd milling around a U.S. military vehicle crash in a busy town center in northeastern Afghanistan, killing two Afghans and wounding more than 50 people, including three U.S. troops, officials said Tuesday.

The U.S. military and Afghanistan's Interior Ministry blamed the attack in the eastern province of Kunar on insurgents and said officials had photographic evidence a Russian-made grenade left over from decades of war was used.

Nevertheless, many wounded Afghans angrily accused the Americans of using a grenade. While the allegation appears to have been discredited, it shows the difficult environment U.S. forces face in trying to win over conservative Afghan tribes that live near the Pakistan border.

A U.S. Army vehicle carrying American troops who help train Afghan soldiers crashed into a concrete median in Kunar's capital of Asadabad, witnesses said.

One shopkeeper, Rohilla, who has a store near the crash, said five or six soldiers got out of their vehicles and tried to pull the truck out of the median with another vehicle.

"Many people gathered around, then there was a blast," said Rohilla, who like many Afghans goes by one name. "It is not clear if the Americans or somebody else threw the grenade. The Americans were busy with their truck accident."

Other witnesses blamed U.S. forces. Rasmatullah, 22, who sells mobile phones, said one of the soldiers "was very uptight. He opened fire with a grenade launcher." Still other witnesses told The Associated Press that a soldier had pulled a grenade out of his pocket and threw it.

The Interior Ministry blamed insurgents, saying in a statement that after women and children had gathered around the disabled vehicle, "the enemy of Afghanistan used this opportunity and threw a grenade into the crowd." The explosion took place in a crowded bazaar near a school and mosque.

A U.S. military spokesman, Chief Petty Officer Brian Naranjo, said the grenade had Russian-language writing on it.

"That for us reinforces that it absolutely was a militant attack," Naranjo said. "That's a Taliban tactic — to throw a grenade into a crowd. No shots were fired and the grenade in question is absolutely not U.S.-made."

At Asadabad's main hospital — where more than 50 people were taken to be treated — Faiz Mohammad Khan, a 60-year-old with a white beard — argued that the Americans must have thrown the grenade because if militants had done it, more U.S. troops would have been wounded or killed. Khan's 18-year-old son was wounded in the attack.

When a patient at a nearby bed was asked how he could be sure U.S. troops had thrown the grenade, Khan angrily barged into the conversation. "The Americans have come here to kill us!" he shouted.

Even the Education Ministry said in a statement that an explosive "from American sources" caused the casualties.

Naranjo said he wasn't surprised that Afghans would make such accusations, "especially if members of the insurgency were in the area."

"We are fighting an enemy that does not follow rules. They not only lie to the local population, but they kill the local population. They do that routinely," Naranjo said.

"We are here to help build these people's lives back. Not cause harm. And we're fighting an enemy that does not have that kind of value system."

A doctor at the hospital, Sayed Ashimi, said two people died in the attack, including a 14-year-old boy, and that the hospital treated about 55 people. Naranjo said three Americans were wounded.

When asked if he thought a militant had thrown the grenade or if the Americans had done it, Ashimi responded: "I think that if it was the insurgents, then the Americans should be dead. But I was not there."

Civilian casualties have long been a source of tension between the Afghan government and U.S. and NATO troops. President Hamid Karzai has pleaded with U.S. officials to reduce the number of civilian casualties.

American officials say that Taliban militants purposely try to cause civilian casualties that can be blamed on U.S. forces in order to turn ordinary Afghans against the international military effort.