KABUL, Afghanistan — While American and NATO forces here are increasingly expressing concern about sophisticated explosive devices apparently entering the country from Iran, Afghan officials are more worried about the human traffic coming over the border.

Since April, Iran has been expelling some of the tens of thousands of Afghan refugees living in that country. While the campaign is officially targeting only those Afghans who entered Iran illegally, there is widespread evidence that Tehran is expelling, sometimes forcibly, legal Afghan residents as well.

Officials in Kabul have already reacted angrily to the decision to send thousands of poor Afghans back to under-resourced western parts of the country, where officials are ill-equipped to deal with the influx. Two Afghan officials were sacked after failing to get the Iranians to change their minds.

The tale told by Noor Ahmad, 34, currently hospitalized in Heart, is common among the returnees. He had been working on a construction site inside Iran when security forces arrived and told him he was being deported. When he didn't react fast enough, a security officer hurled him off the two-story building.

Despite the injuries he sustained in the fall, Ahmad said he was swiftly expelled from Iran, leaving behind his family to an uncertain fate.

He remains bitter about his experience there. "Iranians ... do not care about humanitarian or ethical issues," he said from his hospital bed. "I will remain an enemy of Iran forever."

According to the office of the United Nations High Commissioner for Refugees, there are at least 920,000 registered Afghan refugees in Iran. Experts estimate that as many as 1 million more may be there illegally.

In March, Iran announced that it would begin expelling Afghans in the country illegally. Within a two-week period, more than 50,000 Afghans were forcibly returned to their home country.

Shamsuddin Hamed, the head of the government department for refugees and returned persons in Herat province, claims that Iran is violating an agreement with Afghanistan with the forced deportations.

"The security forces in Iran are treating Afghan refugees in a manner that is neither Islamic nor humanitarian. We have recorded cases of beating, torture and even killings," he said.

Iran's ambassador to Afghanistan, Mohammad Reza Bahrami, denied the allegations.

"The security forces of Iran respect humanity, and the story that an Afghan refugee was killed by Iranian security forces is mere rumor," he said.

Bahrami insisted Iran is only deporting those Afghans who had illegally entered the country, a position contested by Hamed.

"The Iranian authorities have arrested Afghans who had tourist documentation and torn up their passports," he alleged. "They have even deported Afghans who held Iranian ID cards. There are more than 2,000 such cases."