A brown substance believed to be curry powder was found scattered in 50 locations at Nijo Castle — a UNESCO World Heritage site in Kyoto — on Tuesday, police said.

The powder was found by a guide near a corridor at Ninomaru Palace, a national treasure, at around 11 a.m. Blots of the powder were also found at other locations, including on walls, in corridors and in a garden.

The police are investigating the incident with an eye toward potential violations of the Cultural Assets Protection Law. They are checking security camera footage and conducting an analysis of the powder.

The powder was not dangerous, according to a simple examination conducted by the Kyoto Municipal Government.

The blots were not seen before the castle opened at around 8:30 a.m., when staff checked around the castle. The landmark had been busy with visitors that morning and guards were not on patrol at the palace.

The castle was temporarily closed for an inspection by the municipal government, according to the police. It was open Wednesday and the palace also welcomed visitors.

"It is a dreadful act to contaminate cultural assets," said Katsuhisa Yokoyama, a deputy head of the castle office.

In February 2015, Ninomaru Palace was vandalized with an oily liquid.

The castle was originally built in 1603 as the official residence of the first Tokugawa Shogun Ieyasu.

The apparent deliberate attack comes amid a spate of recent vandalism targeting several historic temples and shrines in Japan, including Zojoji Temple in Tokyo and Shimogamo Shrine in Kyoto — also a UNESCO World Heritage site.

Last week, police said they had obtained arrest warrants for two Chinese women for allegedly defacing Meiji Shrine in Tokyo earlier this month.