The Islamic State terrorist group has claimed responsibility for murdering a Christian convert in Bangladesh, says an online group that monitors extremist activity, the latest killing declared by the militant group in the South Asian nation.

Islamist violence has surged in recent months in Muslim-majority Bangladesh, but the government has rejected Islamic State's claims of involvement, blaming political opponents instead. The U.S.-based SITE Intelligence Group said Islamic State had asserted that it killed the man on Thursday in Jhenaidah, a district about 100 miles (161 km) west of Dhaka, the capital, because he converted from Islam.

"Soldiers of the caliphate were able to eliminate the apostate, named 'Samir al-Din', by stabbing him with a knife," SITE quoted the group as saying.Police said they were unaware of the claim, adding that a village doctor with a different surname had been stabbed to death the same day.

"We are not aware of any claim from any terrorist groups. We are trying to nab the attackers," district police chief Hasan Hafizur Rahman told Reuters by telephone.Although the man had converted to Christianity, he later switched back to Islam, Rahman added.

Islamic State has claimed responsibility for the killings of foreigners, attacks on mosques and Christian priests in Bangladesh over the last few months, but police said home-grown militant group Jamaat-ul-Mujahideen is behind the attacks.

The government has denied that Islamic State has a presence in the country of 160 million people. It blames Islamist political opponents for instigating the violence.