Central election officials in Azerbaijan say voters have overwhelmingly approved proposed constitutional changes put forth in a controversial referendum held Saturday, but Azerbaijan's political opposition rejects the claim and says it is preparing a formal protest over alleged cases of fraud.

The electoral officials say voters in Azerbaijan have handed President Geidar Aliyev a resounding endorsement for constitutional change.

The officials say 97 percent of the country's more than four million voters approved proposed amendments to change the way the president and parliament are elected in the former Soviet Republic.

Final results are not expected to be announced until later this week.

Azerbaijan's main opposition parties have said all along they will never accept the vote. And today, leaders of the groups said they are preparing a formal protest about what they say were widespread cases of ballot-rigging and vote fraud.

International observers have yet to comment on Saturdays vote, though they did express concern about the potential for fraud in the run-up to the referendum.

President Aliyev said the changes were needed in order to bring Azerbaijan's 1995 constitution up to Western standards.

The opposition alleges that the principle aim of the vote was to enshrine changes that would make it easier for the ailing president to hand over power to his son.

Speaking to reporters after casting his vote Saturday, President Aliyev said he had no such plans. The president, twice elected in votes criticized as fraudulent, reiterated that he plans to run for a third term.