DHAKA, Bangladesh -- The Islamic State of Iraq and Syria (ISIS) has claimed responsibility for gunning down an Italian aid worker in the diplomatic quarter of Bangladesh's capital, according to an intelligence group that monitors jihadist threats.

The claim by the Sunni extremist group could not immediately be verified independently, but if confirmed would mark its first attack in Bangladesh, a secular country with a predominantly Muslim population. The South Asian nation has been struggling in recent months with the rapid rise of hard-line Islamic groups, banning several that have been blamed for killing four bloggers this year.

Police in Dhaka, the capital, said they had no leads in tracing the three unidentified assailants who, riding on a single motorcycle, drove up alongside Italian citizen Cesare Tavella and shot him Monday night.

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"We have no idea, we can't say anything definitively for now," police official Mukhlesur Rahman said, declining to comment on the ISIS claim of responsibility. "Let the investigation happen."

Initial evidence suggested the attack was planned, police said, noting that nothing had been taken from Tavella during the attack.

ISIS said in a statement dated Monday that a "security detachment" had tracked and killed Tavella with "silenced weapons" in Dhaka, according to the SITE intelligence group's website. It was not immediately clear how close the witnesses were to the attack or how the gunshots could have been heard if a silencer was used.

ISIS warned that "citizens of the crusader coalition" would not be safe in Muslim nations. Almost 90 percent of Bangladesh's 160 million people are Muslim.

Witnesses said they heard at least three gunshots and saw the attackers flee after Tavella fell to the ground, according to police. Tavella was taken to a nearby hospital, where doctors declared him dead.

Italian Foreign Minister Paolo Gentiloni said Monday evening in New York that "we are working to verify" ISIS' claim. The ministry said Tuesday that it was continuing to work with Bangladesh's government on the matter.

Tavella had been working in Dhaka for ICCO, a Netherlands-based church cooperative, serving as program manager of a project focusing on food security and economic development for people living in rural areas in Bangladesh, according to ICCO's website.

Tavella, a veterinarian in his early 50s, had spent extended periods of time traveling around the world giving instruction on how to raise animals, according to Italian media reports. He left for Bangladesh in late August and had a daughter.

Reports indicate he hadn't spent much time in Italy recently, at least extended periods, and that he last lived in central Italy above Ravenna.

The United States and Britain have warned their citizens to be cautious in Bangladesh, with both saying they had "reliable information" that Western interests could be targeted and urging their citizens to limit their movements in the country. The statements did not elaborate on the intelligence.

Over the weekend, Australia's national cricket team delayed its planned tour in Bangladesh over security concerns. The tour has not been rescheduled despite assurances from Bangladesh's government that the players would have a full security detail.

Dhaka police were questioning witnesses, including street beggars who allegedly heard the gunshots and saw the attackers flee, local broadcaster Somoy Television said Tuesday.

One of the witnesses, Sitara Begum, said she was terrified upon hearing the shots while she was sitting on the road at an intersection the near the scene of the attack.

"I was looking at the east side of the road, but hearing the gunshots I looked at the west side and saw two men run and get onto a waiting bike. They fled quickly," Begum said.

Despite the government's banning of several radical Islamic groups from Bangladesh, intelligence sources have confirmed that several hard-line groups are active in the country. The local group Ansarullah Bangla Team, which has apparent links with al Qaeda on the Indian subcontinent, has claimed responsibility for killing four bloggers who criticized Islam's Prophet Muhammed and radical Islam.