Death threats were issued to ten church leaders in northern Bangladesh last week, insisting that those who preach Christianity "must leave this world one by one".

According to persecution charity Open Doors, an anonymous letter was received on November 25 by Rev Barnobas Hembrom of the Bangladesh Baptist Church Sangha in Rangpur.

It read: "Those who are preaching Christianity in Bangladesh must leave this world one by one", and listed the names of nine other pastors working in and around the city.

The police have since provided protection at Hembrom's church and increased security measures in the region.

A police spokesperson told Al Jazeera that the source of the letter is being investigated, but it is believed to have come from an area in northern Rangpur.

The incident follows a rise in targeted shootings of Christians in Bangladesh. Father Piero Parolari, an Italian missionary doctor, was shot and wounded in an ambush in Dinajpur on 18 November, and Italian aid worker Cesare Tavella was fatally shot on September 29.

Kunio Hoshi, a 65-year-old Japanese citizen, was also gunned down four days later by masked men on a motorcycle. Reports suggested that he had converted to Islam three months before the incident.

Islamic State have claimed responsibility for all three shootings, in addition to two others, and many priests in northern Bangladesh have been placed under military protection. An increase in Islamist violence in the country has also seen the targeting of atheists, and four atheist bloggers have been killed in the past year.

There are around 3,000 churches in Bangladesh, but more than 90 per cent of the population is Muslim, and despite a constitutional guarantee of free speech, atheism remains taboo.