The extremists began by asserting control over women’s bodies.

In the political vacuum that has emerged after the overthrow of Bangladesh’s authoritarian leader, religious fundamentalists in one town declared that young women could no longer play soccer. In another, they forced the police to free a man who had harassed a woman for not covering her hair in public, then draped him in garlands of flowers.

More brazen calls followed. Demonstrators at a rally in Dhaka, the capital, warned that if the government did not give the death penalty to anyone who disrespected Islam, they would carry out executions with their own hands. Days later, an outlawed group held a large march demanding an Islamic caliphate.

As Bangladesh tries to rebuild its democracy and chart a new future for its 175 million people, a streak of Islamist extremism that had long lurked beneath the country’s secular facade is bubbling to the surface.

In interviews, representatives of several Islamist parties and organizations — some of which had previously been banned — made clear that they were working to push Bangladesh in a more fundamentalist direction, a shift that has been little noticed outside the country.

The Islamist leaders are insisting that Bangladesh erect an “Islamic government” that punishes those who disrespect Islam and enforces “modesty” — vague concepts that in other places have given way to vigilantism or theocratic rule.

Officials across the political spectrum who are involved in drafting potential amendments to the Constitution acknowledged that the document was likely to drop secularism as a defining characteristic of Bangladesh, replacing it with pluralism and redrawing the country along more religious lines.