WASHINGTON - Human-rights groups on Monday urged the United States to offer emergency sanctuary to Bangladeshi writers targeted by Islamic extremists for their secular beliefs following a wave of killings that have fueled concern over rising radicalism in the South Asian nation.

A coalition of rights organizations, led by the PEN American Center, made the appeal in a letter to Secretary of State John Kerry.

They warned that a group of writers, bloggers, and publishers are in "urgent danger." Four bloggers and a publisher have been killed this year, and dozens more have been publicly threatened.

Bangladesh is a Muslim country with traditions of secularism and tolerance. But a Dec. 8 report on violent extremism prepared for the U.S. Agency for International Development says that since 2013 "there seems to be greater acceptance of the militant groups" within Bangladesh.

The report by Management Systems International, a U.S.-based international development firm, says conservative and less tolerant interpretations of Islam appear to be gaining ground.