Hamas has denied that rocket attacks target civilians
The firing of rockets into Israel by Hamas militants in the Gaza Strip amounts to a war crime, a prominent human rights group has said.
Human Right Watch (HRW) said Hamas should "publicly renounce" the attacks and hold those responsible to account.
HRW said while it had also criticised Israel over its actions in Gaza, "violations by one party to a conflict never justify violations by the other".
A Hamas spokesman has dismissed the group's allegations as "biased".
The 31-page report, Rockets from Gaza, covers the period after November 2008, when Hamas and other militant groups resumed attacks after an Israeli incursion into Gaza.
Three Israeli civilians have been killed in such attacks and dozens injured, with some rockets hitting targets as far as 46km (28 miles) from the Gaza Strip.
HRW programme director Iain Levine said the attacks by Hamas were "unlawful and unjustifiable, and amount to war crimes".
"As the governing authority in Gaza, Hamas should publicly renounce rocket attacks on Israeli civilian centres and punish those responsible, including members of its own armed wing," he added.
Although the number of attacks has decreased in recent months, HRW said they remain "an ongoing threat to the nearly 800,000 Israeli civilians who live and work in range of the rockets".
The report says that the installation in Israeli towns of bomb shelters and early warning systems, giving up to 45 seconds' notice of attacks, has limited the number of casualties.
HRW says rocket attacks are an ongoing threat to Israeli civilians
But it adds that the rockets have still "taken a psychological toll on the population", a violation of the laws of war prohibiting attacks intended to spread terror among civilians.
HRW also accuses Hamas of putting Palestinians at risk by launching attacks from built-up areas.
It said that although more people have been killed in Gaza than in Israel, "violations of the laws of war are not determined by the number of civilian casualties".
Hamas spokesman Ismail Ridwan was quoted by the Associated Press as saying the report was "biased".
"Hamas did not use human shields and did not fire rockets from residential areas," he said. "Hamas does not target civilians."
More than 1,000 Palestinians are known to have died in the conflict while 13 Israelis were killed by either rocket attacks or in so-called friendly fire.
Israel says 12,000 rockets and mortars were fired at it between 2000 and 2008 - nearly 3,000 in 2008 alone.
It says the three-week assault on the Gaza Strip, ending 18 January 2009, was proportionate and intended to bring an end to the attacks.