Police in Pakistan have used batons and tear gas to disperse protesters trying to stage a rally against cartoons satirising the Prophet Muhammad.
The authorities banned rallies in Lahore after protests turned violent
The government banned public rallies in the central province of Punjab after violence in the provincial capital, Lahore, last week left two people dead.
Dozens of Jamaat-e-Islami party members have been held, some before the rally.
BBC correspondents say the protests have become a clear political challenge to President Pervez Musharraf.
Pakistan's powerful six-party Islamist alliance, the MMA, has called for rolling demonstrations ahead of a visit by US President George W Bush next month.
A senior MMA leader, Qazi Hussain Ahmed, was placed under house arrest ahead of the rally planned in Lahore on Sunday.
30 Sept 2005: Danish paper publishes cartoons
10 Jan 2006: Norwegian publication reprints cartoons
31 Jan: Danish paper apologises
1 Feb: Papers in France, Germany, Italy and Spain reprint cartoons
4-5 Feb: Danish embassies in Damascus and Beirut attacked
6-12 Feb: Twelve killed in Afghanistan protests
13-18 Feb: Violent protests break out across Pakistan
18 Feb: 16 killed in Nigerian protest
19 Feb: Police tear gas demonstrators in Islamabad, Pakistan
The BBC's Barbara Plett in Lahore says the authorities are doing everything possible to prevent another mass rally in Lahore, with a huge security presence in the city.
Between 100 and 200 activists managed to reach the centre by hiding in buildings overnight but police have moved quickly to make arrests.
The protests are clearly not just about the cartoons, our correspondent says, but are a confrontation between the government and Pakistan's Islamic parties.
The Islamists have seized on popular anger generated by the cartoons to call for an end to Gen Musharraf's military rule and his close alliance with the US.
Lahore police chief Khawaja Khalid Farooq told reporters nearly 15,000 police officers and 3,000 paramilitary troops had been deployed to prevent demonstrations.
"Nobody will be allowed to violate the ban. Anyone who tries to hold a rally or a protest will be arrested on the spot," he said.
Officials told the BBC that police baton charged a couple of hundred protesters who gathered outside the headquarters of the Jamaat-e-Islami party.
Police broke up a similar assembly near a religious school and fired tear gas to prevent protesters entering the city.
The cartoons depicting the Prophet Muhammad, first published in Denmark in September, have angered Muslims across the world. Five people have died in protests across Pakistan.