Iranians were to vote on Friday in the second round of legislative elections expected to tighten the conservatives' grip on parliament after reformists were hurt by pre-poll disqualifications.
Around 21 million Iranians out of an electorate of 44 million are eligible to vote to choose MPs for the 81 seats in the 290-seat chamber which were not decided outright in the first round on March 14.
The most closely watched competition will be in Tehran, where in the first round conservatives won all 19 of the seats decided outright. Eleven seats are still available and reformists will be hoping to pick up a handful of these.
Under Iranian election law candidates needed at least 25 percent of the vote to be elected outright in the first round. Polls for the second round run-offs were to open at 8:00 am (0330 GMT) and close at 6:00 pm (1330 GMT).
The authorities published no official figures over the share of seats after the first round, but out of the 209 MPs who were elected directly at least 130 were conservatives, more than 30 reformists and the remainder independents.
Although conservatives are assured of holding an overwhelming majority in the parliament, the new MPs are not expected to always give their fellow conservative President Mahmoud Ahmadinejad an easy ride.
Ahmadinejad has infuriated many more moderate conservatives with his expansionary economic policies -- which economists blame for Iran's high inflation -- and his increasingly virulent attacks on opponents.
"The eighth parliament (since the 1979 Islamic revolution) will not be an opposition parliament but it will be a critical parliament," conservative analyst Amir Mohebian told AFP.
Reformists complained bitterly after hundreds of their best candidates were disqualified in pre-election vetting for not meeting the criteria required of MPs, including loyalty to the Islamic revolution.
They also protested after the first round that the results did not reflect their performance, especially in Tehran, but the complaints were discounted by the electoral authorities.
The West reacted with suspicion after the conservative victory in the first round, which the United States described as "cooked."
But with an estimated 42 often well-placed reformist hopefuls competing for the remaining seats out of a total of 162 candidates they are expected to retain a respectable minority.
Reformist analyst Mashallah Shamsolvaezin said: "The situation of reformists is better than in the first round.
"They are at the top of the candidates list now. The Tehran list includes well-known individuals -- some of them used to be high-ranking officials."
The vote takes place after an extraordinary week in Iranian politics.
Ahmadinejad has been locked in a public and bitter row with parliament speaker Gholam Ali Hadad Adel over the implementation of past legislation and has replaced his economy minister, Davoud Danesh Jaafari.
Interior Minister Mostafa Pour Mohammadi is also to step down just days after the election, officials have said, despite criticism that the change comes too close to the polls.
As he left office, Jaafari launched a withering attack on Ahmadinejad, accusing the president of concerning himself only with "peripheral" issues.
Ahmadinejad faces a re-election battle in the summer of 2009 against a background of discontent over high inflation rates, and his toughest competition is expected to come from more moderate fellow conservatives.
Possible rivals include Tehran's ambitious technocratic mayor, Mohammad Baqer Qalibaf, former nuclear negotiator Ali Larijani and parliament speaker Hadad Adel.