Tuesday night's Asian Champions League (ACL) clash between Jeonbuk Motors and Cerezo Osaka was marred when a banner, raised by several Jeonbuk fans before kick-off, read "We celebrate the big earthquake in Japan" in Japanese.
It was taken down during the first half after Cerezo officials noticed and complained to match officials. The team filed a complaint with the Asian Football Confederation (AFC) following the match, which the host side won 6-1.
Cerezo club president Nobuyoshi Fujita, said: "There are heartless people anywhere in the world, and we don't blame all of Jeonbuk's supporters for this incident. But as representatives of Japan, it's our responsibility to report this to the AFC."
Jeonbuk Motors released a statement on its website, apologizing for the incident.
"We officially apologize to all the football fans around the world for the misbehaviour of some fans during the match," the club statement said.
"Although we won, we're deeply regretful for the behaviour of a few fans. We apologize to the Japanese people and promise to take steps to prevent such an incident from happening again."