Jakarta, Indonesia (CNN) -- The gunmen who fatally shot three police officers at a station in Indonesia's North Sumatra province are tied to a militant training camp, authorities said Wednesday.
Men on motorcycles entered the police compound about 1 a.m. and shot the officers, who were on duty at the district police station in Deli Serdang, said. District Police Chief Inspector General Oegroseno.
Oegroseno, who goes by one name, spoke on local television.
The killings raised speculation about a link to recent police raids and the arrests of suspected terrorists in North Sumatra.
It's clear the gunmen who killed police officers were part of a militant training camp in Aceh, which authorities raided earlier this year, Police Chief Bambang Hendarsono Danuri said.
"This wasn't a retaliatory attack [against the string of police raids and arrests in recent days]," Danuri said. "They have plans to assassinate security authorities, certain officials, the police chief. They've identified certain targets".
On Sunday, Indonesian authorities killed three suspects and arrested 15 others in raids. Ties were later established between the 18 and terrorist groups, police said Monday.
The raids netted TNT and high-powered weapons, police said.
The three suspects who were killed Sunday, and three of those arrested, were involved in a bank heist in August, Danuri said.