Bullets and tear gas were fired at demonstrators from an opposition alliance calling for Khaleda Zia, the prime minister of Bangladesh, to step down.
Clashes were reported in about a dozen places across Dhaka as protesters attempted to block main roads into the capital. Stones were thrown at police and several vehicles were set on fire.
At Kanchpur on the southeastern outskirts of Dhaka, police fired rifles and used tear gas and batons when about 3,000 opposition activists gathered on a highway leading to the capital, witnesses said. At least 30 people, including police officers, were wounded in Kanchpur, according to an Associated Press reporter.
In Savar town outside Dhaka, police used tear gas and batons to disperse several thousand people, wounding at least 100, United News of Bangladesh reported.
Similar clashes were reported in Tongi and Gabtali, the two other key entry points to Dhaka in the north. At least 30 people were wounded at Gabtali, UNB said.
At Tongi, police charged demonstrators with batons, leaving at least 50 people wounded, ATN Bangla reported.
Violence also broke out in Dhaka's central Dhanmandi and Kalabagan districts, close to Hasina's office.
“Police attacked peaceful demonstrators,” said Abdus Shahid, an opposition MP, who suffered a leg wound during the violence.
Authorities had deployed about 20,000 security officials in and around the city in an attempt to prevent any violence, the country’s police chief said. He called the attempted siege "illegal" and "undemocratic.”
Police had toured Dhaka overnight with loudspeakers announcing that the High Court had banned the blockade and anyone taking part could be prosecuted.
Nearly 5,000 opposition activists and suspected criminals had been detained by police before the protest, but the main leaders remained free.
The 14-party opposition alliance, led by Sheikh Hasina, a former prime minister, accuses the government of corruption and authoritarianism. The group claims the government is trying to use the election commission to guarantee victory in the poll planned for January 2007. The government denies the charges.
The opposition has launched a campaign of general strikes and street protests to demand the resignation of Zia's four-party coalition government and call for an early election as well as election commission reforms.
Zia has vowed to remain in power until October, when her government's five-year term expires.