Investigators in Houston have determined that a fire at a mosque that broke out Friday was intentionally set, the fire department said Saturday.

The fire at the Savoy Mosque was reported at around 2:45 p.m. local time (3:45 p.m. ET) on Christmas and swelled to two alarms, causing “significant” damage, the Houston Fire Department said.

No one was hurt, but there were about 200 people inside the mosque in southwest Houston about an hour before the fire began, NBC affiliate KPRC in Houston reported.

Related: ‘Suspicious’ Fire Breaks Out at Houston Mosque on Christmas Day

The federal Bureau of Alcohol, Tobacco, Firearms and Explosives had earlier said the fire appeared suspicious because it had multiple points of origin. The fire department’s classification of the fire as “incendiary” means that accidental or natural causes have been ruled out.

There have been no arrests, but the ATF, Houston Police, and the FBI are also investigating the fire along with the fire department’s Arson Bureau.

The Houston chapter of the Council on American-Islamic Relations called on authorities to investigate a possible bias motive in the case, citing what it called a “recent spike in hate incidents targeting mosques nationwide.

A mosque in Coachella, California, was damaged in an intentionally set fire on Dec. 11. A 23-year-old man was arrested and has been charged with a hate crime in that fire. Vandalized mosques have also been reported in Arizona and Georgia.