Gunmen shot dead 10 Afghans working for the international demining organisation the Halo Trust in an attack on their camp in the north of the country, Halo said on Wednesday.
Halo did not attribute blame for Tuesday's attack, saying only that an "unknown armed group" carried it out. Afghan officials blamed it on Taliban insurgents.
Reuters had earlier erroneously reported that Halo had said the Taliban were responsible for the killings.
The insurgents, fighting to overthrow Afghanistan's foreign-backed government, denied involvement in the attack on the camp in the northern province of Baghlan, where fighting has been heavy in recent weeks.
"The Taliban brought them into one room and opened fire on them," provincial police spokesman Jawed Basharat said.
The United Nations called for a full investigation to "ensure that those responsible for this horrendous attack are held accountable and brought to justice," U.N. spokesman Stephane Dujarric told reporters in New York.
The Halo Trust, the largest demining organisation in Afghanistan, said in a statement that unidentified gunmen attacked the camp and killed 10 of its staff.
It said 16 people were wounded. There were 110 workers at the camp at the time of the attack, it said.
After decades of conflict, Afghanistan is strewn with mines and unexploded ordnance and agencies have been working to clear them in the years since the Taliban were ousted in 2001.
An official in the area said most of the surviving workers fled to nearby villages after the attack and police were working to help them.
A Taliban spokesman denied involvement in the killings. But a senior government official in the capital Kabul dismissed that, saying: "This was clearly execution by the Taliban."
The Taliban often attack demining workers because, government officials say, the workers often help to defuse roadside bombs that the insurgents have planted.
Violence has increased across Afghanistan since the United States announced plans in April to pull out all of its troops by Sept. 11.
The Taliban are fighting government troops in 26 out of 34 provinces, and the insurgents have recently captured more than 10 districts, government officials say.
"The United Nations is committed to staying and delivering in Afghanistan. Aid workers, particularly women, are facing increased attacks and harassment as they go about their work," Dujarric said.
"Parties to the conflict in Afghanistan are strongly urged to protect civilians, aid workers, and civilian infrastructure, including schools and hospitals, in compliance with international humanitarian law," he said.
In another incident, an Afghan army helicopter crashed in Wardak province, to the west of Kabul, on Wednesday, killing three crew members on board, the defence ministry said.
The Taliban said its fighters had shot the helicopter down but the ministry said the helicopter was trying to make an emergency landing after developing a technical problem when it crashed.