The Friday march on Dhaka was being organized by the Committee for Resisting Atheists and Renegades. It is supported by other Islamic groups.
Officials said the blockade had virtually cut off the town, which is in the center of Bangladesh's main tea-growing district in the northeast.
"We have decided to call off the blockade to allow tens of thousands of Moslems to march to Dhaka on Friday from this end of the country," committee leader Moulana Habibur Rahman said.
He called for a day-long strike in Sylhet district on Aug. 9 in a continuing campaign against Nasrin and her supporters.
Rahman, head of the radical Khelafat Majlis, fueled the anti-Nasrin campaign earlier by announcing a 50,000 taka ($1,250) reward for her death.
Rahman later denied offering the reward but police issued an arrest warrant for him, sending him into hiding. "We are mystified why police are not arresting him now," a Sylhet journalist told Reuters after Rahman addressed his followers Thursday. Police declined to comment.
Nasrin, a physician-turned-writer in her early 30s, became the target of Moslem fury in Bangladesh when she was quoted by an Indian newspaper as saying that Islam's holy book, the Koran, should be revised thoroughly.
She denies having made this statement.
Nasrin has said in the past that Islam treats women as slaves and that marriage is nothing but slavery for women, remarks which triggered widespread protest and condemnation.
The government has issued an order for Nasrin's arrest, charging her with insulting Islam and hurting Moslem religious feelings. She has since been in hiding.
Meanwhile, in the main port city of Chittagong, students opposed to Islamic fundamentalism clashed with police during two days of street battles that killed six people, doctors and witnesses said.
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