By Nidal al-Mughrabi

GAZA (Reuters) - Human Rights Watch accused the Islamist Hamas government in Gaza on Thursday of failing to investigate the summary executions of seven Palestinians alleged to have spied for Israel during a brief war last November.

Ihab al-Ghusain, head of the Hamas government media office, denied the allegation and said an inquiry headed by the prosecutor general was set up shortly after the incidents and had made recommendations to the cabinet. He did not elaborate.

The slain men were serving prior jail sentences for passing information to Israel when, HRW said, gunmen pulled them from their cells and killed them. Some of their corpses were dragged in Gaza's streets by motorcycles to chants of "God is Great".

One of the men was killed on November 16 and his body was left for the public to see on a busy street. The other six were killed and mutilated four days later.

Following the incidents, Hamas deputy leader Moussa Abu Marzouk called the killings "unlawful" and said the perpetrators "should be punished and it must not be repeated".

Human Rights Watch said their convictions may have been based on evidence extracted through torture, and that an inquiry into their deaths pledged by Hamas seems not to have begun.

"Hamas's inability or unwillingness to investigate the brazen murders of seven men makes a mockery of its claims that it's upholding the rule of law in Gaza," said Sarah Leah Whitson, Middle East director for the New York-based HRW.

"Even before the killings, the abuses the men suffered made the criminal justice system a travesty, regardless of their guilt or innocence," she said.

Hamas and other militant groups were at the time fighting an eight-day conflict with Israel in which six Israelis, two of them soldiers, and 175 Palestinians, mostly civilians, were killed. Human Rights Watch and other groups faulted both Gaza fighters and the Israeli military for causing civilian deaths.

Hamas accused HRW of being "unprofessional," contacting them only a day before their report was published and not focusing enough on Israel. "(HRW) should pay more attention to crimes by the (Israeli) occupation and the killing of hundreds of Palestinians with no mercy," Ghusain told Reuters.

Israel regularly employs Palestinian agents to scope out targets and militant personnel for air strikes, which often kill civilians. Collaboration with Israel is generally reviled by Palestinians, who regard suspected spies as traitors to their people and ostracize their entire families.

On March 12, Hamas authorities launched a month-long campaign calling for collaborators with Israel to turn themselves in to authorities in exchange for amnesty.

The ultimatum expired on Thursday and the Hamas interior ministry said that in the coming hours security forces would arrest a number of spies whom they say failed to surrender.

(Writing by Noah Browning; editing by Mark Heinrich)