Clashes between police and Islamist protesters in the Bangladeshi capital Dhaka have left at least three people dead and 60 injured.
Up to half a million Hefazat-e Islam supporters gathered in the city, where rioters set fire to shops and vehicles.
The activists are calling for those who insult Islam to face the death penalty.
Later, the police used tear gas, rubber bullets and stun grenades to expel thousands of protesters who occupied the city's main business district.
Thousands of Islamist activists were seen fleeing the Motijheel area, and by the early hours of Monday morning police had taken control of the area, reports the BBC Bengali service reports.
On Sunday, throngs of protesters blocked main roads, isolating Dhaka from other parts of the country.
Chanting "Allahu Akbar!" ("God is greatest!") and "One point! One demand! Atheists must be hanged", the activists marched down at least six main roads as they headed for Motijheel, AFP news agency reported.
The area around the city centre's largest mosque turned into a battleground as police reacted to stone-throwing rioters with tear gas, rubber bullets and truncheons.
Three people were killed, the BBC Bengali service reported, with at least one dying of gunshot wounds. Other agencies reported the death toll had risen to at least 10, with several casualties sustaining gunshot wounds to the head.
Reports spoke of some 60 people being injured, including two local TV journalists.
Hefazat-e Islam wants greater segregation of men and women, as well as the imposition of stricter Islamic education.
The group's opposition to a national development policy for women has angered women's groups.
Hefajat-e-Islam draws its strength from the country's madrassahs, or religious schools.
But the government, which describes Bangladesh as a secular democracy, has rejected the group's demand for a new law on blasphemy.
Prime Minister Sheikh Hasina said current legislation was adequate.
A Hefajat-e-Islam activist, Hossain Soliman Abdullah, said the main aim of the protest was to press for the implementation of a 13-point demand inspired by the Koran.
Dhaka's Daily Star newspaper reports that the group hired at least 3,000 vehicles, including buses, lorries and minibuses to bring demonstrators into the capital, while others travelled there by train.
On Friday, Sheikh Hasina said the government had already met many of the group's demands.
"Many of these have already been implemented while some are in the process," she was quoted as telling the Daily Star.
She said the government had already arrested four bloggers for making "derogatory comments" against the Prophet Muhammad and they would be punished if found guilty.
Muslims make up nearly 90% of the country's population with the rest mostly Hindus.