Volker Turk told an emergency meeting of the UN Security Council there must be an independent and transparent investigation of the two attacks in Lebanon on Tuesday and Wednesday where these devices exploded, reportedly killing 37 people and injuring more than 3400 others.
"Those who ordered and carried out these attacks must be held to account," he said.
Lebanon blames Israel for the attacks, which appeared to target Hezbollah militants but also resulted in many civilian casualties, including children.
Before the meeting, Israel's UN ambassador Danny Danon was asked by reporters about speculation Israel was behind the two explosions.
Ambassador Danny Danon said Israel would do everything it could to minimise civilian casualties. (AP PHOTO)
"We are not commenting on the specific attacks you mentioned, but I can tell you that we will do everything we can to target those terrorists to minimise casualties for civilians," he replied.
Lebanese Foreign Minister Abdallah Bouhabib accused Israel of terrorising the entire Lebanese population on streets, in markets, shops and their homes where their communications devices exploded.
Bouhabib insisted Israel not only launched the attacks but told the council there were "official declarations" and a tweet by an adviser to Prime Minister Benjamin Netanyahu "that was lately deleted, emphasising the responsibility of Israel and praising the positive results of this assault".
Danon criticised the Lebanese minister for never mentioning Hezbollah and said the Lebanese people were "trapped in the grip of this terrorist organisation".
Turk, the UN high commissioner for human rights, said the explosions not only violated international human rights law but also appeared to violate international humanitarian law's key principles in carrying out attacks: distinction between civilians and combatants, proportionality, and precautions.
International law also prohibited the use of booby-trap devices that looked harmless, he said, and "it is a war crime to commit violence intended to spread terror among civilians".
"Let me be clear - this method of warfare may be new and unfamiliar," Mr Turk said, "but international humanitarian and human rights law apply regardless and must be upheld".
Danon blamed Iran and its "puppet" Hezbollah for the military action across the Lebanon-Israel border.
"While Israel is not seeking a wider conflict, let me be clear: we will not allow Hezbollah to continue its provocations," he said.
Israel would do "whatever it takes" to return its 60,000 citizens who fled their homes in the north because of attacks, "and we will not allow Hezbollah's terror to dictate the future of our nation".
Iran's UN ambassador Amir Saeid Iravani countered that "Israel bears full responsibility for the perpetration of such horrific crimes", and said his government would pursue accountability for the attack on the country's ambassador to Lebanon, whose eyes were injured in the explosions on Tuesday.
