GAZA CITY, Gaza Strip — Masked Hamas police beat and detained members of the Gaza Strip's tiny Shiite community during a religious commemoration last week, a follower and local rights groups said Tuesday, accusing their Islamist rulers of religious intolerance.

It was the first claim of harassment by a group of Shiite worshippers against the territory's mainstream rulers, who are Sunni Muslims. Hamas officials, who have close ties with Shiite Iran, denied the allegations.

A man who described himself as a Shiite said police burst into a house where followers were marking Arbaeen, commemorating the end of 40 days of mourning following the anniversary of the death of Imam Hussein, the grandson of the Prophet Muhammad. The man said about 15 worshippers were beaten and detained.

He declined to be identified, fearing further harassment. But some of the men filed complaints to the Gaza-based Palestinian Center for Human Rights and the rights group Mezan, which both sharply condemned Hamas over the attack.

Mezan said in a statement that during Saturday evening's incident in the town of Beit Lahia, police smashed up the apartment, broke the bones of seven of the men, detained some of them at a police station and beat them again before sending them to a military hospital for treatment.

"The attack is a violation of the freedom ... to practice one's faith," said Mezan official Samir Zakout.

Interior Ministry spokesman Ihab Ghussein said Tuesday that police stormed the apartment of a group of "outlaws" who were planning "criminal acts." He said he was unaware of the presence of any Shiites in Gaza. He said his offices would look into right groups' allegations that the men were beaten.

There are no official statistics on the number of Gaza's Shiites. They are believed to number several dozen — a minuscule minority among a population of 1.6 million people who are overwhelmingly Sunni Muslim, including the territory's Islamist militant Hamas rulers.

In many parts of the Middle East, Shiites and Sunnis have had strained relations due to deep theological differences that date back centuries. These differences have boiled over into violence over the years in places like Iraq and Pakistan.

Despite such strains, the attack in Gaza seemed surprising, given Hamas' traditionally warm ties with Iran. The fundamentalist Shiite government in Iran has given hundreds of millions of dollars, as well as military training and other backing, to Hamas.