"We will not participate in the December 18 polls unless our chief Begum Khaleda Zia is freed unconditionally and all charges against her are withdrawn," Khandaker Delwar Hossain, the BNP secretary-general, said on Sunday.
He said the party would press its demands during a meeting on election preparations with the interim administration, which has vowed to clean up politics and governance before holding elections.
Earlier, both BNP and its ally Jamaat-Islami Bangladesh requested the election commission to defer the October 15 deadline for party registration by another week.
A delegation to the commission said that the parties were scheduled for a dialogue with the interim administration on Tuesday, making it impossible for them to register by Wednesday.
"It would be difficult for the party to complete registration by October 15, as it was to sit in dialogue with the government a day before," said a letter sent to the election commission by BNP's Hossain.
The commission is expected to detail the election schedule, including dates for filing and withdrawing candidacies, some time in the first week of November.
The Awami League in a separate statement said it would not join the election unless Hasina, now on medical parole in the US, was granted "complete freedom".
It wanted all charges against her dropped.
Hasina was implicated in five cases, including extortion charges, after the military-backed interim administration was installed in early January 2007.
A high court panel earlier rejected her bail request in the case filed by businessman Noor Ali, who alleged that Hasina and two of her relatives extorted more than $700,000 from him for a power-plant concession in 1997.
Hasina, who heads the opposition Awami League party, was prime minister between 1996 and 2001.
A separate court in Dhaka asked Khaleda to appear by October 16 for questioning in a corruption case.
Khaleda has appealed to have the charges against her involving a coal mine, dismissed.
Khaleda's 15 former cabinet members during 2001 and 2005 were also accused of corruption.