By MacDonald Dzirutwe
HARARE (Reuters) - Zimbabwe's Supreme Court has ordered President Robert Mugabe to call by-elections by the end of August, a ruling that could alter the balance of power in parliament between his ZANU-PF party and its rivals.
The case was taken to court by three opposition MPs who lost their seats in 2009 when they were expelled from a splinter wing of Prime Minister Morgan Tsvangirai's Movement for Democratic Change (MDC).
The High Court ordered by-elections to be held but Mugabe appealed to the Supreme Court, arguing the government had no money to conduct the polls.
However, in a unanimous decision made public on Friday, the Supreme Court dismissed Mugabe's appeal and ordered "new elections to fill the vacancies as soon as possible, but no later than August 30, 2012".
It gave no reason for the decision and did not say whether elections should be held only for the three expelled or for another 30 seats vacant in the upper and lower houses of parliament because of the deaths of sitting members.
The MDC holds 96 seats in the 210-seat lower house of parliament, 10 short of a simple majority, against ZANU-PF's 91. The original three constituencies are all in Tsvangirai strongholds.
A parliamentary election is expected within 12 months. Tensions are running high between ZANU-PF and the MDC, part of a power-sharing coalition government cobbled together after a 2008 vote marred by violence blamed on ZANU-PF.
The two parties are also quarrelling over a new constitution now in its third year of drafting.
Mugabe is one of Africa's longest-serving leaders and has been accused of hanging on to power through vote-rigging. The 88-year-old has denied reports of ill-health and says he is fit enough to contest the next presidential election.
(Reporting by MacDonald Dzirutwe; Editing by Ed Cropley)