Hassan Fadlallah, a Hezbollah politician, said on Thursday the group targeted civilians in Israeli cities in response to Israeli attacks that killed hundreds of Lebanese civilians.
"We do not deny that we have bombarded Israeli cities, settlements and infrastructure. But this was always a reaction," he told Aljazeera. "It was a natural reaction. When a state is invaded, it must defend itself."
Nearly 4,000 rockets were fired into northern Israel by Hezbollah during July and August, killing at least 39 civilians.
Firing rockets into urban areas in Israel violated international laws that call for distinction between civilian and military targets, Amnesty International (AI) said.
No grey area
"Targeting civilians is a war crime. There's no grey area," said Larry Cox, AI's executive director in the US.
Fadlallah said that AI had probably come under US and Israeli pressure to criticise Hezbollah's actions during the after issuing a similar report against Israel last month.
The human rights group has called for the UN to begin an inquiry into possible atrocities committed by both sides during the 34 days of fighting.
Hezbollah fired inaccurate rockets packed with thousands of metal ball bearings that sprayed out to maximise harm to civilians, the report said.
"The act was begun by Israel," Fadlallah said. "How could we confront the Israeli aggression? With roses? The resistance [Hezbollah] said that the bombardment of Haifa was in response to the bombardment of Dahiya [Beirut's southern suburbs]."
The human rights group had previously called on the Lebanese militia to release two kidnapped Israeli soldiers and abstain from firing at civilians.
The report is Amnesty's most extensive criticism of Hezbollah since the conflict began, and comes after it accused Israel of violating international law with indiscriminate and disproportionate attacks on civilian targets in Lebanon.
At least 39 Israeli civilians were
killed by Hezbollah rockets
The London-based organisation said in a report issued last month that Israel's attacks on civilian infrastructure during the recent war in Lebanon constituted war crimes, and that Israeli assertions that such attacks were lawful were "manifestly wrong".
Fighting between Israel and Hezbollah began after fighters seized two Israeli soldiers in a cross-border raid on July 12.
The conflict left more than 1,000 people dead, mostly Lebanese civilians - about a third of them children, Unicef said.
AI is preparing another report studying whether Hezbollah contributed to civilian deaths in Lebanon by hiding among civilians, Nicole Choueiry, a spokesman for AI in Britain, said.
It remains to be seen whether either side will face war crimes charges.
Israel and Lebanon both reject the jurisdiction of the International Criminal Court in The Hague, making prosecution there unlikely.