Dhaka: Bangladesh announced the first arrests on Monday over the murder of an Italian aid worker as the government insisted its political rivals rather than the Islamic State group were behind a spate of deadly attacks.

Police paraded four people detained over last month’s killing of 50-year-old Cesare Tavella along with a motorbike said to have been used as a getaway vehicle in the shooting late last month in Dhaka.

The detainees are Minhajul Islam Russell alias Bhagne Russell, Russell Chowdhury alias Chakti Russell, Shooter Rubel, and Shakhawat Hossain Sharif.

The killing near the capital’s diplomatic zone was the first of a series of attacks to be claimed by the Islamic State group and was followed days later by the gunning down of a Japanese farmer in northern Bangladesh.

Speaking after the four suspects were paraded before the media on Monday, Dhaka police said that they had all admitted killing Tavella on ‘the orders of a so-called big brother who offered them money’.

‘They carried out the murder to embarrass the government, to put the government under pressure and to create anarchy,’ Dhaka police commissioner Asaduzzaman Mia told reporters in a press conference.

 ‘Big brother’

 Police described two of the suspects as drug addicts who have previous criminal convictions while another was a drug-dealer and the fourth was ‘a cold-blooded killer’.

They did not however elaborate on the identity of the ‘big brother’ said to have ordered the killing of Tavella who worked for a faith-based Dutch charity.

The 50-year-old Tavella was shot dead on September 28 near Dhaka's diplomatic zone, one of a series of recent attacks which have been claimed by IS.

A Japanese farmer was also murdered by gunmen in northern Bangladesh less than a week after Tavella's killing.