Police officials in Bangladesh said Monday that they arrested four people, three of whom were believed to be the killers of an Italian aid worker shot dead in the capital Dhaka last month. While the Islamic State group claimed responsibility for Cesare Tavella's killing, the authorities dismissed it, calling it an isolated incident. 

"We have arrested four people in connection with the murder of Cesare Tavella. Three of them were his killers," Muntashirul Islam, a spokesman for the local police, said, according to the Agence France-Presse (AFP), adding: “We have also recovered a motorcycle used in the killing.”

Islam added that, according to AFP that the bike was used to escape after killing Tavella. Islam also said that a news conference will be held later Monday, to discuss details of the arrests.

Tavella, 50, worked for a Dutch faith-based charity in Dhaka and was shot dead near the capital city’s diplomatic zone on Sept. 28.

On Oct. 3, ISIS also claimed responsibility for the killing of a Japanese man, Kunio Hoshi, 65, in Rangpur district, about 210 miles from Dhaka. Officials in the country said that Hoshi was killed by three masked men on a motorcycle. Four people have so far been detained for Hoshi’s murder. The motive of the attack against the foreign nationals was not clear, but ISIS threatened more attacks in the country.

"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," ISIS tweeted, according to Reuters.

While attacks against foreign nationals in the country are rare, the increase in violence by Islamist groups has led Western embassies as well as South Korean and Japanese embassies to issue warnings to its nationals to take care of their personal security. Several bloggers, including a U.S. citizen of Bangladeshi origin, have been hacked to death over the past few months as the country witnesses a rise in the Islamist violence.

Bangladesh has since increased security for foreign nationals in the country, by deploying more forces to protect them.