A doctor was hacked to death and his friend critically wounded by men wielding machetes in western Bangladesh, police said.
It was the latest attack on the country's atheist bloggers, minorities and others who promote liberal views.
Local police chief Proloy Chisim said the two were struck on Friday by three attackers who fled on a motorbike in the western district of Kushtia.
The Islamic State group claimed responsibility. Its news agency Amaq said that Sanaur Rahman, a homeopath doctor, was attacked because he promoted Christianity.
The claim could not be verified independently. Bangladesh authorities deny that the Islamic State group has any presence in the country.
The recent killings by suspected Islamist extremists have heightened concerns about the safety of advocates of secularism and free speech in Bangladesh.
Mr Chisim said Mr Rahman, 60, and the second victim, Mohammed Saifuzzaman, were intercepted at a quiet spot near Kushtia town by the attackers. Police recovered a machete from the scene. The area is nearly 160 miles (260km) west of the capital, Dhaka.
Mr Rahman was known to villagers as a kind doctor who provided free treatment and medicines to the poor people.
He and Mr Saifuzzaman both followed the mystic Baul philosophy of Sufi Muslims.
Mr Saifuzzaman teaches at the state-run Islamic University.