Among the offences listed by PHR are "attacks on medical personnel; damage to medical facilities and indiscriminate attacks on civilians not involved in the fighting".
The report further says: "Israel placed numerous obstacles in the course of the operation that impeded emergency medical evacuation of the sick and wounded and also caused families to be trapped for days without food, water and medications.
"The actions ... violate directives of international law which forbid attacks on medical centres and medical teams during fighting" and "blatantly violated codes of ethics."
The PHR report is the latest in a string of accusations relating to the conduct of the Israeli army during the Gaza offensive.
Lieutenant-General Gabi Ashkenazi, Israel's army chief of staff, dismissed on Monday allegations that civilians were killed during the assault, based on soldiers' testimonies published last week.
"I do not believe that IDF troops hurt Palestinian civilians in cold blood," he said in a speech.
"We will wait the outcome of an investigation, but my impression is that the IDF acted morally and if such cases did take place they were isolated."
During the offensive, Israeli fire killed 16 Palestinian medical personnel and wounded 25 others while eight hospitals and 26 primary care clinics were attacked, according to figures from the United Nations and the PHR.
Among the specific incidents cited by the PHR report is that of a "Mr Shurrab" whose two sons were shot by Israeli forces while they drove towards the southern city of Khan Younis on January 16.
"One of the sons died immediately, the other bled to death for 12 hours," PHR said.
"All that time the Israeli soldiers were within a short distance from the Shurrabs but did not provide any assistance despite the father's repeated requests."
PHR condemned the Israeli army, which it said "flaunts its morality", for "declining to help evacuate injured civilians and trapped families, when soldiers acted in a trigger-happy manner as they opened fire on ambulances, medical installations and medical personnel".
Dani Filc, PHR's chairman, said: "We have noticed a stark decline in IDF [Israeli Defence Forces] morals concerning the Palestinian population of Gaza, which in reality amounts to a contempt for Palestinian lives.
"It is critical that the investigation of Operation Cast Lead is completed by a neutral, external investigator without ties to the IDF."
The Israeli army said it was investigating the claims in a "thorough" manner. It insisted that soldiers were instructed to "act with the utmost caution in order not to cause harm to medical vehicles and medical facilities".
In a statement, the Israeli army blamed Hamas for putting health personnel and medical facilities in harm's way.
"We have noticed a stark decline in IDF morals concerning the Palestinian population of Gaza, which in reality amounts to a contempt for Palestinian lives"
"Throughout the fighting, Hamas methodically made use of medical vehicles, facilities and uniforms in order to conceal and camouflage terrorist activity, and in general used ambulances to carry terror activists and weapons," it said.
"Hamas used ambulances to "rescue" terror activists from the battlefield and used hospitals and medical facilities as hiding places".
Such actions "greatly complicated the co-ordination of rescue and medical evacuation", the army said.
"It must be emphasised that under international law, the protections afforded to medical teams or "protected institutions" ... cease to exist when these medical teams or institutions are not used for humanitarian purposes rather for carrying out actions intended to harm the state of Israel".