TOKYO (AFP) - A Japanese tourism agency said Wednesday its website was hijacked by hackers who displayed a message purportedly from the Islamic State in Iraq and Syria (ISIS) group, less than two months after the group claimed to have beheaded two Japanese hostages.

The hack follows a series of similar attacks on websites including a community futsal team and a Tokyo camera shop, public broadcaster NHK reported.

The Nishinomiya Tourism Association, near the major city of Osaka, said its home page started displaying what appeared to be a black-and-white ISIS logo late Sunday evening.

"Hacked by Islamic State (ISIS). We are everywhere ;)," a message read in English alongside the logo.

The association said it temporarily took the site offline on Monday to fix the problem. It has since been restored to its original format, according to an agency official, adding that it remained unclear who was behind the attack.

"We have reported the incident to police who are reviewing what happened," she told AFP on Wednesday.

ISIS militants claimed in a video earlier this year that it had killed respected war correspondent Kenji Goto, a week after the group said it had also beheaded his friend Haruna Yukawa, a self-styled contractor.

In one clip, the ISIS executioner warned that Goto's killing would mark the beginning of "the nightmare for Japan".

The officially pacifist country has long avoided involvement in Middle East conflicts and has rarely been touched by religious extremists.

The hostage drama erupted after Japanese Prime Minister Shinzo Abe pledged US$200 million (S$2.8 million) in aid for refugees fleeing ISIS-controlled areas in Syria and Iraq during a tour of the Middle East. Militants had demanded the same sum in exchange for the pair, whom it had been holding for months.