Deadly rocket and mortar fire on Israeli cities by Palestinian militant groups in Gaza during a May conflict constituted war crimes, Human Rights Watch said Thursday.
The New York-based rights group analyzed attacks from Gaza that resulted in the deaths of 12 civilians in Israel and injuries to dozens more.
Rockets that misfired or fell short also killed or wounded "an undetermined number of Palestinians in Gaza," the group said, with at least seven Palestinian civilians killed.
Hamas spokesman Hazem Qassem rejected the accusation.
"The resistance exercised its natural right to defend its Palestinian people," he told AFP.
The rockets were launched during an 11-day conflict that saw Israel pound Gaza with air strikes as militants in the blockaded enclave fired more than 4,000 rockets towards Israel.
Israeli strikes killed some 260 people in Gaza, including militants, while munitions from Gaza killed 13 people in Israel, including a soldier.
The report comes a day after the UN Palestinian refugee agency UNRWA condemned "the existence and potential use by Palestinian armed groups" of tunnels under its schools in Gaza, saying they placed pupils and staff "at risk".
The condemnation followed a demand by Israel's ambassador to the United Nations, Gilad Erdan, to freeze UNRWA's funding after Israeli public television reported Hamas blocked UN inspectors from inspecting a tunnel near an agency-run school.
Human Rights Watch previously accused Israel of war crimes for strikes that killed dozens of civilians despite "no evident military targets in the vicinity" during the conflict that ended with a May 21 ceasefire.
In Thursday's report, the rights group cited statements by Gaza's Islamist rulers Hamas and other militant groups announcing barrages of rockets at Tel Aviv and other Israeli cities.
After one such statement, shrapnel from a rocket killed a 63-year-old Israeli woman south of Tel Aviv. Another rocket killed a father and his teenage daughter in a village about 20 kilometers (12 miles) from Tel Aviv.
"Under international humanitarian law ... warring parties may only attack military objectives," Human Rights Watch said, adding, "launching such rockets to attack civilian areas is a war crime."
Hamas spokesman Qassem said the accusations were "unfortunate," because "the real crimes were committed by the occupation by targeting civilians in the recent aggression on the Gaza Strip, killing more than 100 children and women and demolishing residential buildings."
Human Rights Watch suggested the International Criminal Court, which is investigating alleged Israeli war crimes, should include "unlawful Palestinian rocket attacks against Israel, as well as unlawful Israeli attacks in Gaza."
In April, Human Rights Watch accused Israel of committing the crime of "apartheid" by seeking to maintain Jewish "domination" over Palestinians in all areas under its control, an allegation Israel rejected.