Nahid Hasan was picked up from Dhaka overnight on suspicion that he was spreading hate and violence on behalf of Islamic State using the pseudonym Jihadi John on a Facebook page, police joint commissioner Monirul Islam said.
“We are verifying whether he actually had contacts with the radical group," Islam said.
The government has consistently denied that Islamic State has a presence in the country and instead blamed religious groups such as the Jamaat for instigating violence in the Muslim but secular nation of 160 million people.
Police said the second man arrested in the overnight raid was believed be behind text messages threatening writers and university teachers who have been targeted by unknown assailants this year.
Tensions have been rising in Bangladesh over the trials of Islamists for war crimes during its struggle for independence in 1971 and some leaders of the Jamaat as well as its ally, the Bangladesh Nationalist Party, have been executed.
Critics say the government is using the war trials to settle political scores.
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