Women mourn outside of a Shia mosque in Brussels.—AP

BRUSSELS: Belgium's Muslim community was in shock Tuesday after a man set fire to a Shia mosque in Brussels, leaving the imam dead in an act some linked to tensions between Shias and Sunnis.

As investigators sought to determine whether late Monday's arson attack was an isolated incident or a deliberate assault on the Shia community, Interior Minister Joelle Milquet suggested inter-religious strife may be to blame.

“This person went in (the mosque) hurling statements linked to the Syrian conflict. It appears to be a problem between Sunnis and Shias,” Milquet said, adding that investigators still had to confirm the motive.

“Belgium will not tolerate this type of act and the importing of this type of conflict on its territory,” she said, adding that the government would take “all necessary measures” in coming days to prevent attacks.

The area around the Brussels mosque, one of four Shia centres of worship in the city's overwhelming majority Sunni Muslim community, has a large immigrant Muslim population.

The suspect told police he was a Muslim born in 1978, but authorities were not immediately able to confirm his identity because he lacked ID papers.

Azzedine Laghmich, an official at the mosque, told AFP the attacker was “a Salafist,” who sprayed petrol inside the mosque before setting it alight and shouting Sunni slogans on his way out —cries related to the conflict in Syria.

“All the eyewitness accounts said so,” Laghmich added.

Isabelle Praile, another senior official in Belgium's organised Muslim community, said the mosque “had already been placed under police protection several years ago,” citing threats from members of the ultra-conservative Salafist movement.

More than 100 men gathered near the Rida mosque after the fire, shouting Shia slogans behind a police tape as some prayed and others hugged or cried over the death of imam Abdallah Dadou, a 46-year-old father of four.

The imam died of smoke inhalation and a second person was slightly injured after the man, who wielded a knife and an axe, set fire to the place with fuel.

“I brought my eight-year-old son here with me so that he can see blind hate, what it can do,” said Ismael Ben Mohammad, 40.

The mayor of the city's Anderlecht ward, Gaetan Van Goidsenhoven, appealed for calm at an overnight press conference, saying it was “not only necessary to live side-by-side, but also to allow justice and the police to do their work.”

The imam was described by worshipper Abdel Adouzeyneb, a 39-year-old real estate agent, as “a person who was loved by everybody —he was open, well integrated, smiling and happy.”

Prosecutor Jean-Marc Meilleur said the arson suspect was detained by police after people inside locked him inside the mosque.

“At the moment, there is only one suspect,” Meilleur said early Tuesday, adding that it was too soon to know whether it was a one-man attack or a wider plot.

The last time an imam was targeted in Brussels was in 1989 when Saudi-born Abdullah Muhammad al-Ahdal was shot dead.

He served as imam in the Grand Mosque of Brussels and was killed on March of that year by an armed man inside the mosque.

His killing was claimed by a small pro-Iranian group in Lebanon who accused him of being too moderate and of having rejected the death fatwa slapped on writer Salman Rushdie.