Paramedics and the man’s family claim that Israeli forces killed a 57-year-old Palestinian teacher who went to treat a militant who was fatally wounded.
Father of six and Jenin refugee camp resident Jawad Bouaqneh was assassinated outside his home.
It happened during a night of raids by the Israeli army in the West Bank’s occupied territory.
His passing brings the total number of Palestinians killed this month to 17, both militants and civilians.
The Israel Defense Forces (IDF) claimed that after receiving a lot of live fire from Palestinian assailants, their troops were under heavy fire.
It said it was aware of a report that a civilian was killed “in the area of the exchange of fire” and the incident was being “reviewed”.
Mr Bouaqneh’s son Farid said they heard a man – later confirmed to be the fatally wounded militant – calling for help outside their home.
“My father went out to help the man, to provide first aid,” he said.
“We dragged him inside and… they shot my father in the upper body and I moved him inside as he was covered in blood,” he told Reuters news agency, standing at a doorway with a blood-stained floor.
Palestinian paramedics said Mr Bouaqneh and a medic were both approaching the wounded militant outside the house.
“At that moment the Israeli soldiers shot high velocity bullets at them and a bullet hit the teacher… in the chest while he was trying to help the injured,” the Palestinian Medical Relief Society (PMRS) said in a statement to the BBC.
“[The medic] said he was wearing a clear first aid vest when the shooting happened,” it said, adding both the men who were shot were declared dead at hospital.
The Palestinian health ministry confirmed the death of Adham Jabareen, 28, who was later identified by Palestinian Islamic Jihad as one of its members. Local reports said he was a commander in Jenin for the group, which is listed by Israel and the West as a terrorist organisation.
Video from Thursday morning’s raid shows armoured troop carriers and a military digger entering Jenin, while repeated gunfire can be heard in other footage.
Palestinian media reported that Israeli snipers were deployed on rooftops of several homes overlooking the camp, while an undercover Israeli unit entered a building at the camp entrance and detained residents.
The IDF said its forces faced gunfire and that explosive devices were thrown, adding that an Israeli soldier suffered minor injuries and was taken to hospital. It said troops seized weapons and arrested an individual “suspected of involvement in terrorist activity”.
It is the latest in a near-nightly campaign of Israeli military search, arrest and intelligence gathering raids that intensified from last April, as violence in Israel and the occupied West Bank reached levels unmatched in years.
Last year in the West Bank more than 150 Palestinians were killed, nearly all by Israeli forces. The dead included unarmed civilians, militant gunmen and armed attackers. A series of Palestinian attacks targeting Israelis, as well as militant gunfire at troops during arrest raids, killed more than 30 people including civilians, police and soldiers.
Also on Thursday US National Security Advisor Jake Sullivan visited the region, meeting Israeli and Palestinian officials, amid growing concern about a further deterioration in the security situation.
It is the first trip by a senior US official since Benjamin Netanyahu returned to office leading the most right wing and religious coalition in Israel’s history.