TOKYO (AP) _ Police suspect someone of using cyanide to poison curried rice served at an annual summer festival, after four people died and dozens of others fell ill apparently upon eating the food, a report said Sunday.

The exact cause of the deaths remains unknown, but vomit from the victims showed evidence of a reaction to cyanide, the Kyodo News service reported.

About 60 people attending the festival Saturday night in central Japan's Wakayama prefecture were sickened after eating the curried rice dish. More than 30 of them were hospitalized, the report said.

The four who died ranged in age from 10 to 64 years old, it said.

Cases of food poisoning from spoiled items are common in Japan, where raw seafood and semi-cooked dishes are popular fare. More than two dozen people have suffered from poisoning linked to tainted salmon roe so far this summer.

An outbreak of the O-157 strain of E. coli bacteria two years ago killed 12 people, mostly small children and elderly people, and sickened 10,000 others.