Afghan officials were hunting on Sunday for Afghan migrants in a river bordering Iran after reports that Iranian border guards tortured dozens and threw them into the water to keep them out of Iran.
Authorities in western Herat province said they retrieved 12 bodies from the Harirud river and at least eight other people were missing.
The incident could trigger a diplomatic crisis between Iran and Afghanistan at a time when the coronavirus pandemic has seen an exodus of Afghan migrants from Iran, with many testing positive. Up to 2,000 Afghans cross the border from Iran, a coronavirus hotspot, into Herat each day.
Afghanistan's foreign ministry said on Saturday an inquiry had been launched. A senior official in the presidential palace in Kabul said initial assessments suggested at least 70 Afghans trying to enter Iran from Herat were beaten and pushed into the Harirud river on Saturday.
Abbas Mousavi, a spokesman for Iran's foreign ministry, said the "incident" took place on Afghan soil.
"Border guards of the Islamic Republic of Iran denied the occurrence of any events related to this on the soil of our country," he said in a statement on Sunday.
Abdul Ghani Noori, governor of Herat's Gulran district, said dozens of Afghan migrant workers were thrown into the river by members of the Iranian army.
"Iranian army men used shovels and gunshots to injure Afghan workers and threw them in water," Noori told Reuters, adding that some of the injured workers were being treated in a hospital.
Doctors at Herat District Hospital said they had received the bodies of Afghan migrants.
"So far, five bodies have been transferred to the hospital. Of these bodies, it's clear that four died due to drowning," said Aref Jalali, head of the hospital. He added that two injured men were brought to the hospital on Sunday evening.
The Taliban militant group, fighting to oust the Afghan government, said Iran should launch an investigation into the killings and "strictly punish the perpetrators".
"We have learned that 57 Afghans on their way to the Islamic Republic of Iran for work were initially tortured by Iranian border guards and 23 of them later brutally martyred," the Taliban said in a statement.
Noor Mohammad said he was one of the Afghans caught by Iranian border guards as they were trying to cross into Iran in search of work.
"After being tortured, the Iranian soldiers threw all of us in the Harirud river," Mohammad told Reuters.
Shir Agha, who said he also survived the violence, said at least 23 people thrown into the river were dead.
Afghan officials that it was not the first time that Afghans had been killed by Iranian police guarding the 920-km (520-mile) border.
As of Sunday, at least 541 coronavirus-infected people in Afghanistan were from Herat province, which recorded 13 deaths, with the majority of cases Afghan returnees from Iran, said Rafiq Shirzad, a health ministry spokesman in Herat.