* Team leaving on Sunday for Egypt, Tunisia and Libya
* Plans to go to Tripoli, Benghazi to gather testimony
* Will cooperate with ICC prosecutor in the Hague
(Recasts with fresh quotes)
By Stephanie Nebehay
GENEVA, April 8 (Reuters) - United Nations investigators said on Friday they would start next week to probe alleged human rights violations committed by all sides in Libya's conflict and share evidence with the U.N. war crimes tribunal.
The independent commission of inquiry said its mandate was to investigate abuses by forces loyal to Muammar Gaddafi, the rebels fighting to topple him, and foreign parties involved in the conflict.
The three-member team, headed by American war crimes expert Cherif Bassiouni, declined to reveal its exact travel schedule but will stop first in Egypt and also visit Tunisia and Libya.
It would gather testimony and evidence widely, including on rape and use of mercenaries, and make every effort to protect witnesses from reprisals.
"We'll talk to everybody. We will be visiting hospitals, so we will be talking to people who are injured, we will be going to prisons, we'll talk to people who are in prison," the Egyptian-born Bassiouni told a news conference in Geneva.
"We will be talking to combatants, civilians, any available source of information will be addressed," he said.
The team would travel to largely rebel-held eastern Libya and the government-held west and attempt to reach besieged towns including Misrata, depending on the security situation. "Our work will be done on both sides with complete impartiality."
It has told the government of its plans and Tripoli issued a statement saying it would welcome them from April 15, according to Bassiouni.
He said the team was cooperating with the International Criminal Court (ICC) in the Hague, whose prosecutor Luis Moreno-Ocampo also is looking into possible war crimes by Gaddafi, his sons and his inner circle.
Moreno-Ocampo has said Libyan authorities had decided they were ready to kill unarmed protestors even before unrest spread from neighbouring Tunisia and Egypt.
"We don't work for the ICC, they don't work for us. We have a mandate, they have a mandate. We have, however, decided that we are going to have a collaborative relationship," Bassiouni added.
The U.N. Human Rights Council, composed of 47 member states, unanimously approved launching the inquiry on Feb. 25. The Geneva forum denounced attacks on civilians, killings, arrests and the detention and torture of peaceful demonstrators, saying they may amount to crimes against humanity.
Bassiouni, asked whether the inquiry would look into any crimes by foreign powers, said: "If you read the mandate, it said human rights violations in Libya. It doesn't say by whom, it doesn't say against whom. Period. Whoever commits a violation will be reported."
"Now, whether that rises to the level of criminal accountability and how this is communicated to the ICC or other, we'll cross that bridge when we reach it," he said.
Libyan government officials say NATO airstrikes have killed civilians, including children, in areas under Gaddafi's control although the alliance says it has not seen evidence that this is the case. NATO said on Friday its aircraft probably killed rebels in a friendly fire incident a day before near the oil port of Brega. Rebels have said five of their fighters died.
The other two panel members are Philippe Kirsch, a Canadian former judge of the International Criminal Court (ICC), and Asma Khader, a Jordanian lawyer and former minister.
Khader, an expert in sexual crimes, said it would look into rapes, including the case of a Libyan woman Eman al-Obaidi who last month accused pro-government militiamen of gang-raping her.
"We all watched the case of Obaidi and we heard that there are other women in the same case. Of course it will be one major part of our investigation."
Editing by Andrew Callus and Michael Roddy