Masked assailants riding a motorbike shot and killed a Japanese man in northern Bangladesh on Saturday, police said, the second foreigner in a week to be gunned down in the South Asian country.

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

Saturday's incident took place at Mahiganj village in Rangpur district, said Rezaul Karim, a police official. The victim was identified as Kunio Hoshi, around 50 years old, he said, adding that Hoshi had started a grass farm in Rangpur, about 300 kilometers (185 miles) north of Dhaka, Bangladesh's capital.

Local residents reported that two bike-riding assailants shot three times at Hoshi on Saturday morning, Karim said. Police have detained four people for questioning in the case, he said.

Mohammad Kibria, an assistant sub-inspector of police in Rangpur, said Hoshi was taken to the emergency unit of the state-run hospital, where doctors declared him dead.

"The dead body has been kept in the morgue. It can be clear after further investigation how and why he was killed," Kibria said.

Ayub Ali, a witness, said three men were standing near a road and fired at Hoshi as he passed by on a rickshaw. "They fired at him while he was on the rickshaw and left the scene," Ali said.

Officials at the Japanese Embassy in Dhaka could not immediately be reached for comment. In Tokyo, the foreign ministry said officials were trying to confirm reports of the incident.

Saturday's killing took place five days after an Italian aid worker was killed by motorbike-riding assailants in Dhaka.

The Islamic State group also claimed responsibility for that attack. Bangladesh's government, however, dismissed the claim, saying there was no evidence. It described that killing as an "isolated incident."

The Italian aid worker, Cesare Tavella, had been working in Dhaka for a Netherlands-based church cooperative, serving as program manager for a project focusing on food security and economic development for people living in rural areas in Bangladesh.

Bangladesh, where most of the population is Muslim, 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.