Police in Bangladesh's capital have banned all rallies and prevented a top opposition leader from leaving her office, while dozens of opposition activists have been detained across the country, officials and local media said Sunday. The moves come ahead of the anniversary of a general election boycotted by a major opposition alliance last year.

Police have cordoned off the office of former Prime Minister and current chief of the Bangladesh Nationalist Party, Khaleda Zia, since late Saturday night in Dhaka's Gulshan area, with authorities saying the measure was part of enhanced security steps. Zia is the archrival of Prime Minister Sheikh Hasina, who came to power last year for a second term.

On Sunday, police clashed with opposition supporters in several parts of the country, including the eastern district of Brahmanbaria, leaving dozens of people injured, ATN Bangla and Channel 24 television stations reported.

Police would not immediately comment on the clashes.

In Dhaka, suspected opposition activists torched a bus and smashed several vehicles, local media reported.

Authorities deployed paramilitary border guards to patrol Dhaka and some other major cities, said Mohsin Reza, spokesman for Border Guards Bangladesh.

Junior Home Minister Asaduzzaman Khan Kamal said Sunday that security for Zia had been upgraded and that she was not confined as claimed by opposition leaders.

Hasina returned to power in an election last Jan. 5 that was boycotted by Zia's party, which said the poll would be rigged.

Police have locked down the headquarters of Zia's party in Dhaka's Naya Paltan area, which remained under tight security.

In a statement Sunday, Dhaka Metropolitan Police said a ban on holding rallies in the capital would remain in effect until further notice because "clashes and untoward incidents" could take place on Monday, when Zia's party had been planning to hold an anti-government rally.

By Sunday evening, Dhaka was cut off from the rest of the country, with the capital-bound buses and ferries shut down due to fears of violence.

Zia has renewed her call for Hasina to step down and declare a new election, but ruling party leaders have rejected the demand, saying the next election will not be held before 2019, when the government's five-year term expires.

The Election Commission had staged the Jan. 5 election last year after two major political alliances led by Hasina and Zia failed to agree on a formula for appointing a caretaker government to oversee the election. Hasina had refused to heed opposition demands to step down and appoint a neutral administration to hold the election and vowed to uphold the constitution by holding the poll.

Chaos had reigned in the country for a year, with opposition activists staging a series of attacks, strikes and transportation blockades that left nearly 300 people dead in 2013.

Zia was prime minister from 2001 to 2006, but failed to hand over power peacefully. A military-backed caretaker government then ruled the country for two years before Hasina came to power with a landslide election win in 2008.