Ms Zia's alliance won just 31 seats in parliament, electoral officials say
Former Bangladesh Prime Minister Khaleda Zia, defeated in Monday's parliamentary elections, has rejected the results saying the vote was rigged.
"We have confirmed reports of rigging and other irregularities in many polling stations across the country," she told reporters in Dhaka.
Election officials said earlier that Ms Zia's rival Sheikh Hasina's Awami League had won a landslide victory.
The poll was mostly praised by media, monitors and the world community.
On Tuesday, at least one person was killed and more than a dozen were injured in clashes between rival political activists in the northern Pabna area, officials said.
The election follows two years of army-backed rule in the country.
In her first reaction to Monday's voting, Ms Zia said she believed the results did not reflect the people's will.
"So we reject the election outcome," she said.
Sheikh Hasina and her allies have pulled off a stunning victory
"We are collecting details of more irregularities and will give them to the media and appropriate authorities over next few days," she said.
Ms Zia's Bangladesh Nationalist Party alliance has complained of fraud and forgery at more than 200 polling stations.
Observers say the next two days will be vital as to whether the result is accepted or sparks violence.
Election officials earlier said that the party of Sheikh Hasina, another former prime minister had secured more than 260 seats in parliament, while Ms Zia's BNP won 31.
The Election Commission has not yet declared a final official result.
There was a massive turnout for the election, which was overseen by hundreds of international monitors who largely pronounced the poll fair and credible.
The win for the Awami League is a dramatic reversal in fortunes for the two parties, says the BBC's Mark Dummett in Dhaka. In 2001, the Bangladesh Nationalist Party won the election overwhelmingly.