"Hamas' claim that rockets were intended to hit Israeli military targets and only accidentally harmed civilians is belied by the facts," the New York-based group said.
HRW issued its statement after the Islamist rulers of the Gaza Strip said its investigations of allegations in a UN report on the Gaza war found that they and other Palestinian armed groups "struck military targets and avoided civilian targets."
HRW pointed out that most of the rocket attacks on Israel hit civilian areas. "Civilians were the target," the rights group said, adding that "deliberately targeting civilians is a war crime."
The UN report into the 22-day Gaza offensive published in September also said the firing of the hard-to-aim rockets at southern Israel deliberately targeted civilians and could constitute a crime against humanity.
The report authored by former international prosecutor Richard Goldstone accused both Israel and Palestinian groups of war crimes during the conflict, which killed 1,400 Palestinians and 13 Israelis.
HRW rejected claims Hamas made during the war that attacks against Israeli civilians were justified reprisals for attacks on Palestinians and lawful resistance against occupation.
The rights group stressed that "under the laws of war nothing can justify an attack against civilians, and violations by one side do not justify violations by the other."
The Goldstone report recommended its findings be referred to the International Criminal Court in The Hague if Israel and Hamas failed to carry out credible, independent investigations.
Israel has rejected the report as "anti-Semitic" despite the fact Goldstone is Jewish, because it accuses Israeli troops of deliberately targeting civilians and destroying vital infrastructure.