Security is high in Pakistan as voters gear up for crucial parliamentary elections overshadowed by violence and fears of rigging.
Monday's polls are set to end an era of military-led rule, but there are fears they could trigger further unrest.
The two major opposition parties say President Pervez Musharraf's allies are planning massive fraud. They have vowed to protest if they suspect foul play.
The worst act of pre-poll violence saw 47 killed at a rally on Saturday.
The elections for the lower house of parliament were originally scheduled for 8 January, but were postponed after the assassination of opposition leader and ex-PM Benazir Bhutto on 27 December.
Polling stations open on Monday at 0800 (0300 GMT) and close at 1700.
'No choice'
A spokesperson for Mrs Bhutto's Pakistan People's Party (PPP), which is leading in opinion polls, said the vote was "not going to be a free and fair election".
The party accused the pro-Musharraf PML-Q of plotting to stuff ballot boxes.
Mrs Bhutto's former rival, Nawaz Sharif, whose party is also ahead of Mr Musharraf's supporters in polls, said a "massive rigging plan" had "been implemented".
Mrs Bhutto's widower and successor as party leader, Asif Ali Zardari, said in an interview with the UK's Sunday Times newspaper that his party would have "no choice but to take to the streets" if the elections were rigged.
However, he was more conciliatory on Sunday, when political rallies were banned and he made a visit to his late wife's tomb in Sindh province, a PPP heartland.
He said: "If God gives us a chance... we will try to take all foes and friends together.
"I think we have reached the breaking point where if we don't band together, we will lose this great nation which we call Pakistan."
Voters' fears
The authorities have stressed repeatedly that the vote will be free and fair.
But President Musharraf has also warned against street protests.
Close to half a million security personnel, including about 80,000 soldiers, have been deployed for the voting.
Saturday's attack took place in the town of Parachinar, near the border with Afghanistan, when a suicide car bomber drove into a crowd of people that had gathered outside the house of a politician allied to the PPP.
On Sunday, four soldiers were killed when their vehicle hit an explosive device in Baluchistan province, police said.
Correspondents say the election turnout may be low as many voters fear further violence.
Analysts say polls suggest a fair vote is likely to result in a hung parliament, with none of the three biggest parties winning a majority.
The BBC's Barbara Plett in Pakistan says that if the PPP then joins forces with pro-Musharraf parties, there may be a backlash within its rank and file, which blames the president for Mrs Bhutto's murder.
But, she says, if it forms an alliance with Mr Sharif's party there could be confrontation with the presidency.
Mr Sharif has refused to work with the president unless he reinstates judges sacked when he imposed emergency rule late last year, in what was widely seen as an attempt to head off a challenge to his re-election as president.
It the two opposition parties jointly gain two-thirds of the seats, they may try to impeach President Musharraf.
Mr Musharraf stepped down as army chief late last year. He has ruled the country since seizing power in a coup in 1999.
The nuclear-armed country is a key ally in the so-called US "war on terror", with President Musharraf's government facing a growing pro-Taleban resistance.
PHOTO CAPTION
Anti-Musharraf protesters, Lahore, Pakistan