Kunio was killed when he was on his way to his grass farm at Kaunia on Saturday morning.

On Sep 28, Italian aid worker Cesare Tavella was killed at Dhaka’s diplomatic zone Gulshan.

Radical group Islamic State has reportedly claimed credit for both the murders.

The terrorist group also threatened more attacks.

"There will continue to be a series of ongoing security operations against nationals of crusader coalition countries, they will not have safety or a livelihood in Muslim lands," the militant group said in a statement posted on their official Twitter account on Saturday.

A high-level meeting on Saturday decided to increase security at homes and work places of foreign diplomats and foreign nationals, Inspector General of Police AKM Shahidul Hoque said.

Tavella and Kunio were killed in the same way – three assailants executed the murder and they fled on motorcycle, witnesses said.

After her arrival from New York on Saturday, Prime minister Sheikh Hasina ordered authorities to track down the murderers as soon as possible.

She said these incidents aimed at destroying Bangladesh’s image.

Home Minister Asaduzzaman Khan Kamal on Saturday night told bdnews24.com that the two murders were linked.

Masked gunmen shot Japanese Kunio thrice, police said.

Police detained four people for questioning over the murder of 66-year-old Kunio.

Detainees are Zakaria Bala, his brother-in-law ‘Hira’, rickshaw puller Monnaf Ali and Murad Hossain.

Kunio was a tenant at Bala’s house at Munshiparha, and Murad lives in a house next to the crime scene.

The victim knew Zakaria Bala’s two brothers who live in Japan.

Bala’s family in Rangpur helped him set up the farm.

The Japanese was travelling to his farm on Ali’s rickshaw.

But Hira, the owner of a fishery next to Kunio’s farm, was not accompanying him as he used to do regularly.

Rangpur’s Additional SP Zainul Abedin told bdnews24.com that the Japanese national had recently visited India and returned to Bangladesh on Aug 28 through Burhimari border check post in Lalmonirhat.

Italian charity worker Tavella’s murder coincided with the visit of the Australian cricket team’s security officials.

The officials were in Bangladesh to assess the security arrangements made for the cricketers whose arrival was delayed over security concerns. Eventually, the tour was postponed.

Several foreign missions in Dhaka have asked their nationals to limit their movements in Bangladesh.