Police in Bangladesh say they have arrested a suspected Muslim militant for his alleged involvement in the killing last month of a gay rights activist and his friend in the capital.

Police identified the suspect as Shariful Islam Shibab, a former member of a banned Islamic group Harkatul Jihad who joined another militant group, Ansarullah Bangla Team, in mid-2015.

Munirul Islam, head of a newly-formed police counterterrorism unit, told a news conference on Sunday that Shibab was arrested in the southwestern district of Kushtia based on evidence from the investigation.

The Bangladeshi branch of al-Qaida had claimed responsibility for the April 25 killing of Xulhaz Mannan, an employee of U.S. Agency for International Development, and his friend, Tanay Majumder.

Only one of 15 such killings has been prosecuted since 2013.