Andiwal initially reported 10 civilians killed, but said later that city officials on the scene had given him mistaken information. He said the five civilian victims included two children. Four more civilians were wounded, he said.
Lt. Col. Paul Fanning, a spokesman for the U.S.-led force in Afghanistan, said one of its troops also was killed. He declined to release the victim's nationality.
The blast came a day after a shooting incident in which two soldiers from the separate U.S.-led coalition were fatally wounded in Helmand. An explosion killed four British troops in the province on Tuesday.
Recent fighting in Helmand and neighboring Kandahar province has demonstrated the resilience of the Taliban-led insurgency, more than six years after a U.S.-led invasion drove the militia from power.
Afghanistan's international backers last week pledged more than $21 billion in additional aid, but stressed that it needed to be spent better to bolster an Afghan government beset by corruption and still with limited authority.
On Friday, NATO and the Afghan troops were rounding off an operation to counter insurgents who had infiltrated a fertile valley within striking distance of Kandahar city, the Taliban's former capital.
The Afghan Defense Ministry said Thursday that the forces had retaken some 10 villages in the Arghandab district and killed 56 insurgents, many of them foreigners - an apparent reference to militants based in neighboring Pakistan. Two Afghan soldiers and one civilian also died.
But Kandahar provincial Gov. Asadullah Khalid said Friday that the insurgent death toll was over 100. He said villagers reported that some militants had spoken the Pashto dialect of tribes from across the border in Pakistan.
"We want to tell the Taliban, especially the Pakistani Taliban, that if they come again they will get the same treatment," Khalid said.
On Friday, an Associated Press reporter saw 19 corpses, some of them missing limbs, of what officials said were militants lying in a pomegranate orchard in Manara, a village in Arghandab.
Officials pointed to a yard-deep crater in a nearby field and to broken and scorched trees that they said were the result of an airstrike.
NATO said the operation had banished any threat to Kandahar and would help reassure Afghans appalled at the embarrassing mass escape of Taliban prisoners from a city jail last week. But the alliance also sought to downplay the insurgents' hold on the area.
"No large formation of insurgents were met or spotted. Only minor incidents occurred," alliance spokesman Maj. Gen. Carlos Branco said. "The insurgents who were there were evidently not in the numbers or with the foothold that they have claimed."
Hundreds of families who fled the lush, orchard-strewn valley that begins just 10 miles from the city can safely return, the alliance said.
Din Mohammed, a farmer walking back to Manara on Friday with 12 family members, said Taliban fighters had been bent on combat.
"They said they wanted to fight the Afghan and foreign forces. I asked them what should I do, but they said they didn't care, so I left everything - my land, my possessions, my animals," Mohammed said.
"Last night I heard on the radio that the Taliban were either dead or gone, so we came home," he said.
Afghan officials had said that some 400 insurgents swept into Arghandab, though NATO insisted that the numbers were smaller and had sought in vain to persuade residents not to flee the region.
Still, the alliance sent 600 British and Canadian troops to support a larger Afghan force, many of whom had been airlifted from the capital, Kabul.
NATO and Afghan officials said ground troops were moving methodically through the area on the east bank of the Arghandab River, wary of bombs and keen to avoid civilian casualties. Mark Laity, another NATO spokesman, said Thursday that mopping-up operations in Arghandab would continue "for a little while yet."
Confidence in the government and foreign forces was badly shaken last week when a bold Taliban attack on the Kandahar prison freed 900 inmates, including 400 Taliban fighters.
"We know that after recent events like the jailbreak there is concern about our capabilities. This was a fast and very effective response and I think something that all Afghans can take great heart from," Laity said.
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Associated Press writers Stephen Graham and Rahim Faiez in Kabul contributed to this report.
