By Ruma Paul
DHAKA (Reuters) - Four protesters were killed in clashes between activists of Bangladesh's ruling party and opposition supporters on Monday and authorities cut off transport into Dhaka on the first anniversary of national polls themselves fraught by violence.
Despite police warnings, opposition leader Begum Khaleda Zia refused to cancel Dhaka rallies planned to mark what her Bangladesh Nationalist Party (BNP) has dubbed "democracy killing day".
Khaleda, a former prime minister herself, has demanded fresh polls under a neutral administration, calling Prime Minister Sheikh Hasina's government "undemocratic and illegal".
The normally clogged streets of Dhaka were nearly empty on Monday afternoon, as authorities cut off bus, rail and ferry services into the city. Thousands of riot police were deployed in anticipation of more unrest.
"Security has been ramped up across the country, including Dhaka, to thwart any untoward incidents," Dhaka district police chief Habibur Rahman told Reuters.
Bangladesh has been in a state of political uncertainty since last January, when Prime Minister Hasina's Awami League came to power for a second consecutive term after a parliamentary election campaign marked by bloodshed. The polls had been boycotted by the BNP and deemed flawed by international observers.
Police said two protesters in their 20s were shot dead in Natore district during clashes between ruling and opposition party activists. The opposition said the victims were BNP activists, though police have not confirmed their identity.
Two more protesters were killed during separate clashes involving opposition and ruling party activists and security forces in the northwestern part of the country.
The opposition leader says she has been confined to her office in Dhaka's diplomatic enclave since Saturday, according to BNP party officials, with armoured vehicles equipped with water cannon outside.
In protest, Khaleda called for an indefinite nationwide blockade of roads, railways and waterways.
"The government has turned the whole country into a prison," Khaleda told reporters.
The government denied Khaleda was being held against her will, and says it has deployed extra security at her office for her protection.
"Who has confined her?" media quoted Hasina as asking at a party meeting on Sunday. "She can go to her residence any time."
Hasina and Khaleda, both related to former national leaders, have nursed a long and bitter rivalry, and have dominated politics in Bangladesh for more than two decades.
BNP officials said hundreds of their supporters had been detained since Saturday. Scores of protesters have been injured in clashes in Dhaka, the port city of Chittagong and elsewhere.
(Editing by Krista Mahr and Ralph Boulton)