The UN expert on the Palestinian territories said Thursday an independent investigation should establish whether Israel committed war crimes in Gaza during its recent offensive. Richard Falk, an independent UN rights expert, said there was compelling evidence that Israel breached basic humanitarian rules and the laws of war by conducting a large-scale military operation "against an essentially defenseless population." "There needs to be an investigation carried out under independent auspices as to whether these grave breaches of the Geneva Conventions ... should be treated as war crimes," Falk said. "I believe that there is the prima facie case for reaching that conclusion," he told reporters in a telephone briefing from California. Israel's Ambassador in the US, Aharon Leshno-Yaar, said in response that "Professor Falk's bias against Israel is well known." "He disqualified himself from being what he is supposed to be, a neutral, balanced and professional rapporteur," Leshno-Yaar told The Associated Press. Falk, a retired American law professor, said the rockets fired from Hamas-ruled Gaza on southern Israel were also a violation of international law. "This is the first time I know of where a civilian population has been essentially locked into the war zone, not allowed to leave it despite the dense population and the obvious risks that were entailed," Falk said. "The civilians in Gaza were denied the option of becoming a refugee." Israel, which has an obligation to protect the civilian population under its occupation, did not even allow children, women or sick people to leave the besieged territory, he added. Over half of Gaza's people are children, Falk said. "In this sense, it almost has the appearance of being a war that is waged directly at the expense of children," he said. The 78-year-old Falk is unpaid and without enforcement power in the UN post, which he has held since May. He previously angered Israel by comparing the Jewish state to Nazi Germany and accusing it of crimes against humanity because of its treatment of Palestinians. He was barred from entering Israel and sent back on a plane to the US in December.