A group of prominent international war crimes experts is calling for an inquiry into the behavior of Israeli forces and Palestinian armed groups during the Jewish state's recent offensive in Gaza. 

The group signing the open letter to U.N. Secretary General Ban Ki-moon and the U.N. Security Council includes Nobel Laureate Archbishop Desmond Tutu and Richard Goldstone, a former chief prosecutor in Yugoslavia and Rwanda.

The letter urges the establishment of a U.N. commission to look into allegations that international humanitarian law was violated, by both sides, during the 23-day offensive.  It calls for a prompt, impartial investigation that would set the record straight and make public any violation of international laws.

The attack, in which Israel targeted militants who have been firing rockets at civilian areas in Israel, killed an estimated 1,300 people, many of them civilians, in Gaza.

The 16 judges and investigators include others who have led investigations in East Timor, Lebanon, Sierra Leone, and Darfur.  The letter said they were "shocked to the core" by events in Gaza. 

Israeli forces have come under criticism for their use of white phosphorus during their campaign in the densely-populated enclave. 

When asked about the open letter, Israeli Prime Minister's office spokesman Mark Regev repeated Israel's assertions that its military followed all the international rules of conflict.

"We made every effort not to target innocent civilians," said Regev.  "On the contrary, we tried to be as surgical as is humanly possible in a difficult combat situation targeting those Hamas extremists who are shooting rockets into Israel, trying to kill our citizens."

The letter came as Israel steps up indirect negotiations with Hamas to reopen Gaza's Israeli-controlled borders and reach a formal truce.  The militant Islamist group that controls Gaza wants Israel to release hundreds of Palestinian prisoners in exchange for Gilad Shalit, an Israeli soldier who was seized by Palestinian militants and taken to Gaza in 2006.

Prime Minister Ehud Olmert's Cabinet has rescheduled a meeting to discuss the matter on Tuesday. 

Mr. Olmert is due to leave office soon.  Members of his centrist government have warned Hamas it may be the group's last chance to secure concessions before a harder-line government under hawkish former Prime Minister Benjamin Netanyahu comes to power.

Officials with Mr. Netanyahu's Likud party say it has initialed a deal for the ultranationalist Israel Beitenu Party to join a Likud-led coalition - putting them one step closer to forming a new government.