The Amnesty International report said that the militant Shiite group fired nearly 4,000 rockets into northern Israel, killing 43 civilians, seriously injuring 33 others.
The guerilla rocket attacks on northern Israel also forced hundreds of thousands to take refuge or flee.
According to the report about a quarter of all rockets, some packed with thousands of metal ball bearings, were fired directly into urban areas.
Amnesty said Hezbollah's firing of 900 "inherently inaccurate" Katyusha rockets into urban areas flouted the principle in international law of distinguishing between civilian and military targets.
Hezbollah chief Hassan Nasrallah and other senior figures, repeatedly stated their aim of targeting civilians as a form of reprisal for the Israeli military bombardment, Amnesty said.
’No justification’
The nine-page document reported that it was only because Israeli civilians fled their homes or took shelter in bunkers that a higher death toll was prevented.
"The scale of Hezbollah's attacks on Israeli cities, towns and villages, the indiscriminate nature of the weapons used and statements from the leadership confirming their intent to target civilians make it all too clear that Hezbollah violated the laws of war," said Amnesty's secretary-general Irene Khan.
"The fact that Israel has also committed serious violations in no way justifies violations by Hezbollah. Civilians must not be made to pay the price for unlawful conduct on either side."
There was no immediate word on the report from Hezbollah while Israeli foreign ministry spokesman Mark Regev refused to comment directly on Amnesty's claims.
Less than a month ago Amnesty International called for both sides of the conflict to be investigated for "grave violations" of human rights law.
The London based human rights group then accused Israel of "indiscriminate and disproportionate" attacks on civilian infrastructure and war crimes.
The report urges that any United Nations inquiry should look in particular at the impact of the hostilities on civilians on both sides with a view to bringing those responsible to account and compensating victims.
UN post attack report
CBC News has reported that Israel had determined its air strike on a UN observer post in Lebanon that killed four international peacekeepers was an error due to an incorrect map.
The air-strike in July on the UN post in southern Lebanon killed the four peacekeepers from Canada, Austria, China and Finland.
CBC News said that it had obtained a briefing by an Israeli official on an internal Israeli military report.
The report concluded the air strike occurred because Israeli ground forces were using an incorrect, hand-drawn map.
Based on information in the briefing, the map used by the Israeli artillery identified the clearly marked UN post in the Khiyam area of southern Lebanon as a Hezbollah base.
Israeli Foreign Ministry spokesman Mark Regev, who gave the briefing to the CBC, was quoted as saying that "the report points to the fact that there was an error on our side in the maps that were done manually at the time of the combat."
CBC News said the briefing reports Israeli forces received a number of warnings from the United Nations urging them to stop shooting so close to the base.
The message was received by Israeli forces on the ground, who stopped firing on the post, according to the Israeli briefing. But apparently the warnings were not received by the Israeli air force, CBC News said.
Spanish troop deployment outlined
The Spanish defense minister and the head of the country's armed forces on have detailed their country's contribution to the UN mission in southern Lebanon.
It came as the first troops neared the port of Tyre.
Spain is providing 1,100 troops in all, the third-largest EU ground force contingent behind Italy and France.
The country will take charge of a multinational brigade including troops from Belgium, Finland, Ireland, Poland and Portugal from their base at Marjayoun in southeastern Lebanon.
Defence Minister Jose Antonio Alonso noted that the deployment, which began on September 8, won the unanimous approval of parliament last week, and stressed that Spain was participating strictly under the UN umbrella.
Army chief of staff General Felix Sanz Roldan said the Spanish advance party of 570 troops were off the coast of Cyprus on Thursday and were due to arrive on a beach, known as Rest House, south of Tyre late Friday morning before reaching their Marjayoun HQ on Monday.