The Israeli military has said it regrets shooting dead an unarmed 65-year-old Palestinian man who, according to his family, was asleep in bed in the West Bank city of Hebron when soldiers mounted a raid in search of Hamas militants.

The Israeli defence forces (IDF) launched an investigation into the death of Amr Qawasme, the fifth Palestinian to die as a result of Israeli military actionsince the start of the year. One death is disputed by the IDF: that of Jawaher Abu Rahma after inhaling teargas fired by soldiers.

Qawasme was killed after being shot in the upper body and face, according to medical sources at the Hebron Governmental hospital who were quoted by the Palestinian news agency Ma'an.

An IDF statement said it happened during an operation to arrest five Hamas militants who were released from a Palestinian prison yesterday. "A Palestinian man who was present in one of the terrorists' homes was killed," the statement said. "The IDF regrets the outcome of the incident." Its investigation would present its conclusions "as early as next week".

According to witnesses, soldiers broke into the house and entered Qawasme's bedroom. His wife, Sobheye, told Reuters she heard shots and found her husband lying in a pool of blood. "I was praying when they entered," she said. "I do not know how they opened the door. They put their hand to my mouth and a rifle to my head."

A Reuters TV video showed bullet casings over the floor of the bedroom and bedding soaked with blood. Qawasme lived on the floor above that of Wael Mahmoud Said Bitar, a Hamas militant. Qawasme's son Raja'e told Ma'an that the soldiers must have thought Bitar was living in the apartment. "They thought it was Wael so they fired bullets immediately after entering my father's room while he was sleeping in his bed; I guess they did not make sure of his identity," he said.

Qawasme's death follows the shooting dead of two Palestinians this week. The IDF said they had tried to cross the border fence between Gaza and Israel. Last Sunday Mohammed Daraghmeh was shot dead at a checkpoint near the West Bank city of Nablus after soldiers mistook a bottle he was holding for a knife and he failed to heed warnings to stop. A military investigation cleared the soldiers.

Jawaher Abu Rahma died last Saturday after the IDF fired teargas at a protest in Bil'in over the Israeli separation barrier. The IDF has rejected hospital reports that she died as a result of tear gas inhalation, saying she may have had a pre-existing medical condition. It has offered no evidence to support its claim.