Zimbabwe's ruling Zanu-PF party and the opposition Movement for Democratic Change have contested half the results of the parliamentary election in March, extending a stalemate that has triggered widespread violence.
Official results showed President Robert Mugabe's Zanu-PF lost its parliamentary majority for the first time since independence in 1980, while the MDC and a breakaway faction together secured enough seats to control the assembly.
The fresh challenge to the election results by the two biggest parties could change the balance of power in the new parliament. The assembly can be sworn in during an electoral court's review of contested seats, but the court can remove deputies later if it overturns any results.
The challenge will have no effect on the result of a parallel presidential ballot, however, which showed MDC leader Morgan Tsvangirai won 47.9 per cent against Mr Mugabe's 43.2 per cent, triggering a run-off since neither candidate won an absolute majority.
The MDC has not said whether it will participate in the run-off. It believes Mr Tsvangirai won the election outright and has ended Mr Mugabe's 28-year rule over the once prosperous country whose economy is in ruins. If he does not contest the run-off, Mr Mugabe is automatically declared the winner
The state-run Heraldnewspaper said Zanu-PF and the MDC had lodged 53 and 52 petitions respectively with the electoral court, citing irregularities they believed had affected the results. The challenges come after a recount of original results in 23 constituencies confirmed Zanu-PF's defeat.
The court has six months to rule on the complaints, which dispute the results of exactly half of the 210 seats in parliament. To cope with the large number of challenges, the newspaper said Chief Justice Godfrey Chidyausiku increased the number of electoral court judges from three to 20.
A day earlier, independent Zimbabwean election monitoring group ZESN expressed doubt about the credibility of the results of the presidential election and accused Zanu-PF of attacking observers.
ZESN, made up of 38 non-governmental organisations, said a one-month delay in announcing the results undermined the impartiality of the Zimbabwe Electoral Commission.