Japan's top government spokesman expressed outrage Monday over the killing of a Japanese citizen who became the second foreigner to be gunned down in Bangladesh in less than a week.

Kunio Hoshi was shot to death by unidentified assailants in northern Bangladesh on Saturday. Bangladesh's government rejected a statement by the Islamic State group claiming responsibility for the attack.

"Such a dastardly act should never be repeated. I feel outraged by such an act," Yoshihide Suga, Japan's chief Cabinet secretary, told reporters in Tokyo on Monday. He extended condolences to Hoshi's family, and said the Japanese government was seeking a full investigation into the case.

Bangladesh has been struggling in recent months with a rise in violence claimed by hard-line Islamic groups, banning several that have been blamed for killing four bloggers this year.

The Islamic State group issued a statement claiming responsibility for Saturday's attack, according to the SITE Intelligence Group, which monitors jihadi postings online. The report could not be independently confirmed. The Islamic State also claimed responsibility for the killing of an Italian aid worker last week in Bangladesh's capital.

"Oh, it's absolutely rubbish, there is no IS in the country, no way," Bangladeshi Home Minister Asaduzzaman Khan told The Associated Press on Sunday. "Why would IS do this here? These are incidents for creating instability in the country."

"The claims are fishy and we are examining," he said.

Khan's view was echoed by Prime Minister Sheikh Hasina, who also dismissed the Islamic State's claims.

"Someone will post something online ... why should we accept that unless we prove that? We cannot accept that," she told reporters.

Following the Islamic State's claim of responsibility for the Sept. 28 killing of Italian aid worker Cesare Tavella, who was gunned down by motorbike-riding assailants in Dhaka, Bangladesh's government said there was no evidence that the extremist group was involved and called it an "isolated incident."

Hasina on Sunday blamed the country's main opposition Bangladesh Nationalist Party and its key ally, Jamaat-e-Islami, for the attacks, accusing the groups of trying to destabilize the country.

However, a spokesman for the BNP refuted the prime minister's charge, saying Hasina's statements were expected and regrettable.

Saturday's attack took place in Mahiganj village in Rangpur district, with local residents saying two assailants shot three times at Hoshi. A third man waited for the pair on a motorbike, and the three then fled together on the bike.

Japanese public broadcaster NHK reported that Hoshi, a 66-year-old farmer from Japan's northern prefecture of Iwate, had operated agricultural projects in that region and near Tokyo.