KABUL, Afghanistan – A demonstration that officials said had begun as a peaceful pro-government rally in southern Afghanistan on Wednesday instead turned into a bloody melee, with as many as 10 people killed and 14 wounded as the police fired on demonstrators.

When it was over, two cellphone towers were charred wrecks, shops in the local bazaar had been burned and a civilian helicopter taking off from a nearby American base had crash-landed. But what was unclear was exactly why: local leaders and officials greatly differed in their accounts of how the violence started.

The Afghan authorities accused the Taliban of infiltrating the rally with gunmen, suicide bombers and motorcycles with bombs strapped onboard, according to Esmatullah Safi, the police chief of Maiwand District in southern Kandahar Province. He said the helicopter, a Russian-made MI-17 used as a civilian cargo transport, either crashed or was shot down during the episode, shortly after it took off from the base.

“The Taliban infiltrated among the protesters carrying AK-47s and bringing some suicide bombers with them,” Mr. Safi said. “Later on, the protesters and some of the Taliban went to a nearby building and started firing at our police forces. Luckily they did not hurt any of our police, but in our exchange of fire we killed seven Taliban and some protesters and wounded 11 others,” Mr. Safi said. Afterward, the authorities said they had found and disarmed bombs strapped to four motorcycles.