LONDON — An arsonist’s attack on a Shiite mosque in a Brussels suburb that left its 46-year-old imam dead provoked shock and grief among Belgium’s Muslim population on Tuesday, but the authorities there attributed the attack to tensions between the Shiite and Sunni communities — not a new case of the so-called Islamophobia hostility that has been rising in Europe.

The victim, identified by Belgian media as Abdallah Dadou, a father of four, died while attempting to extinguish the blaze, which was set late Monday night at the mosque in the Brussels suburb of Anderlect. Earlier a man who identified himself as a Muslim had approached the building carrying an axe, a knife and flammable liquid that he spread in the mosque, setting fire to it, officials said. The mosque was heavily damaged.

Joëlle Milquet, Belgium’s interior minister, condemned the attack but said that authorities had for the most part discounted the idea that it was motivated by anti-Islamic hate groups. Rather, she said, it appeared to be “a problem between Sunnis and Shiites,” according the Web site of Le Libre Belgique, the Belgian daily newspaper. “But I remain cautious because the judicial authorities still need to confirm a number of things,” she said.

Sunnis comprise the overwhelming majority among immigrant Muslims in Brussels. Jean-Marc Meilleur, spokesman for the prosecutor’s office in Brussels said the suspect, apprehended by local people who turned him over to the police, was awaiting formal charges.