The death of 30-year-old Jaradat sparked widespread protests in the West Bank.
"The death of a prisoner during interrogation is always a cause for concern, but in this case, when Israel has shown a pattern and practice of prisoner abuse, the need for outside, credible investigation is more urgent than ever," Richard Falk, UN special rapporteur for human rights in the occupied Palestinian territories, said in a statement.
Falk, an American law professor serving in the independent post, suggested the United Nations Human Rights Council might set up an international forensic team to investigate Jaradat's death.
Jaradat was arrested some 10 days ago on suspicion of throwing stones at Israeli cars in the West Bank. His death in an Israeli jail last Saturday, together with a hunger strike by four other prisoners, led to rioting in which six Palestinians were injured. One of them, a 15 year-old boy, was in critical condition.
Palestinian officials say an autopsy showed Jaradat died of extreme torture. Israel says the autopsy was inconclusive.
Falk said Dr Saber Aloul, the Palestinian Authority's chief pathologist who observed the autopsy, had found "clear signs of torture on the body of the previously healthy 30-year-old Jaradat".
"In light of Dr Aloul's findings that there was no evidence of heart disease or damage, and that there were signs of torture on Jaradat's body, an independent international investigation should be launched," Falk said.
The office of UN High Commissioner for Human Rights Navi Pillay urged Israel to conduct a full inquiry and reveal its findings.
"We strongly encourage Israeli authorities to carry out a prompt, independent and impartial investigation into his death. The results should, in our view, be made public," Pillay's spokesman Rupert Colville told Reuters on Wednesday.
"If reports suggesting he died from torture turn out to be true, then Israel must hold the perpetrators accountable by bringing criminal charges," Colville said.
For nearly a year, Israel has boycotted the Geneva forum, accusing it of long-standing bias against Tel Aviv.
On March 18, the council is due to take up a report by UN investigators who called on Israel last month to halt settlement expansion and withdraw all half a million Jewish settlers from the occupied West Bank, saying that its practices could be subject to prosecution as possible war crimes.
The United States, Israel's main ally, accuses the council of unfairly singling out Israel.
"Until this Council ceases to subject Israel to an unfair and unacceptable bias, its unprincipled and unjust approach will continue to tarnish the reputation of this body, while doing nothing to support the progress toward the peace among Israelis and Palestinians that we all desire so deeply," Esther Brimmer, US assistant secretary of state, told the talks on Tuesday.
GENEVA (Reuters) -- A UN human rights investigator called on Wednesday for an international inquiry into the weekend death of Arafat Jaradat, who Palestinian officials say was tortured to death in Israeli custody.