Amnesty International is claiming its team sent to investigate human rights abuses has been denied access to Jenin refugee camp.
The delegation, including a British forensic pathologist, was sent to the devastated West Bank town to gather evidence about the fate of those who died during recent fighting.
Professor Derrick Pounder was part of the three-person team which he said was refused entry to the camp or Jenin Government Hospital by Israeli forces.
The University of Dundee expert said help was urgently needed for people trapped under buildings after fierce fighting.
He said: "There are two urgent tasks. The first is the humanitarian task of gathering evidence to identify the dead so that the bodies can be given to the families.
"The second is to obtain forensic evidence about the causes and circumstances of death which will clarify what has been happening in Jenin camp. International human rights and humanitarian law require that forensic investigations are conducted in this respect.
"The refusal to allow us to conduct or even to assist in enabling others to conduct such investigations is very serious and gives rise to questions about the authorities' motives."
The delegation also includes Mr Javier Zuniga, from the international secretariat of the human rights body, and Kathleen Cavanaugh from the Department of Law at Galway University in Ireland.
Amnesty International had argued that with only a small number of forensic experts in Israel and among Palestinians, none of whom are in Jenin or the camp, the bodies would deteriorate and provide less evidence about how people had died.
The group is now considering legal action in Israel to gain access to Jenin refugee camp and hospital.