KABUL, Afghanistan — Coalition forces said Sunday that they were investigating allegations that more than 50 civilians were killed in a recent operation in a remote part of northeast Afghanistan.

The International Security Assistance Force denied that civilians had been hurt in the four-day operation last week in the largely Taliban-controlled district of Ghazi Abad in Kunar province, insisting that only insurgents were killed.

Civilian casualties, most often caused by airstrikes, are a source of deep tension between the U.S.-led international coalition and the government of President Hamid Karzai. The coalition has altered its operating methods to try to reduce accidental deaths, which undermine public support while it tries to fight a raging insurgency.

Mohammad Shah, a 38-year-old resident of Ghazi Abad district, said that 70 people had been killed or injured in the operation, which he said involved Afghan and U.S. troops. He said coalition forces blocked a road to the area following the attack, hampering efforts to get the wounded to hospital.

“”After the attack, the road was closed by American soldiers. Only after an appeal by the district chief was one vehicle allowed through to get the injured,”” said Shah, speaking by phone from a hospital in the provincial capital, Asadabad. “”Nine of my relatives were injured.””

Because of the roadblock, Shah said, help managed to get through only on the afternoon of the day after the attack. The wounded in his family included three children, ages 2, 6 and 8. He said that the 2-year-old had lost a leg below the knee. The child and a badly injured woman were taken to a hospital to Jalalabad, in neighboring Nangarhar province, and the others were being treated at the hospital in Asadabad.

The coalition said that it had video of the incident, which showed 36 insurgents, carrying weapons, being killed. Nevertheless, it was sending an assessment team to the area to investigate the charges of civilian casualties.

Maj. Michael Johnson, a spokesman for ISAF, said helicopters were involved and they had fired bullets, rather than missiles, at the insurgents.

“”We gained positive identification before firing,”” Johnson said. “”We had plenty of indication that this was a group of bad guys on the side of a mountain. This was a very rugged area. We have no concern about collateral damage based on where it was located.””

In the past, some reports of high civilian casualties have been met with initial ISAF denials, but the coalition later has had to admit responsibility.

The Kunar provincial governor, Fazlullah Wahidi, said 51 civilians and 13 insurgents had been killed, along with 13 insurgents. He said the dead civilians included 26 children. He put the number of injured at seven.

“”There are foreign Taliban fighters in that area,”” Wahidi said. “”Coalition forces and Afghan army had faced resistance, so they asked for air support.””

Asadullah Fazli, the provincial director for health, said that the seven injured, including four children, arrived at the provincial capital’s hospital on Friday night. Sunday morning another wounded person was admitted to the hospital.

Mea Hasan Adil, head of the provincial council, said government control extended no farther than the main town of Ghazi Abad district.

“”The rest of the district is under the Taliban. People there favor the Taliban more than the government,”” said Adil.

According to a United Nations report last year, 2,412 civilians were killed and 3,803 injured in the conflict in Afghanistan in the first 10 months of 2010. However, the insurgents were responsible for 76 percent of those casualties, the UN found. The report attributed 742 civilian deaths and injuries to coalition or Afghan government forces, which was down 18 percent from the comparable perion in 2009.

Separately Sunday, the death toll from a Taliban suicide bomb and gun assault on a bank in Jalalabad the day before climbed to at least 38. An Interior Ministry spokesman, Zemeri Bashary, said that among the dead were 21 members of Afghan security forces, at the bank to collect their monthly salaries, and 17 civilians, Seventy-one others, mostly civilians, were injured.

A supermarket and a shopping center in Kabul were attacked in recent weeks.

“”Unfortunately, we see that there’s a change of tactic in the terrorist attacks and they are targeting soft targets,”” Bashary said at a news conference in Kabul.