Critics say Mugabe has crammed the Supreme Court with his supporters

A government minister said that Judge Ebrahim, who was the last non-black judge on the Supreme Court, had announced his retirement without giving any reasons.

He is expected to leave the bench in May, Justice Minister Patrick Chinamasa told the pro-government newspaper The Herald.

No comment has yet been reported from the judge himself.

Of south Asian origin, Judge Ebrahim has been on the Supreme Court since 1990.

In early 2000, he sat with four other judges, two white and two black, but the government subsequently made accusations of pro-white bias and added three black judges.

The two whites, Chief Justice Anthony Gubbay and Judge Nicholas McNally, had both left the court by December last year after clashing with the government over its failure to halt violent attacks on white-owned farms.

Government officials have attacked the Supreme Court's ruling on the electoral amendments, describing it as a "rotten fish".

Election fever

On Saturday there were large rival rallies in the southern city of Bulawayo.

Thousands of Mr Mugabe's Zanu-PF supporters turned up at a stadium to hear the president speak.

He said that his policy of reconcilation with the country's former white rulers after independence had been an error.

"Did we make a mistake through reconciliation? Yes, deep down I say it was a mistake," said Mr Mugabe.

We must make an effort to make sure that we have the highest turnout... we must confirm a resounding defeat for this regime

Morgan Tsvangirai

At a rally a few miles away, opposition leader Morgan Tsvangirai told thousands of his own supporters that they should not fear intimidation.

"We were determined to bring change to this country because there were some of us who were murdered in order to bring this democratic change," the Movement for Democratic Change (MDC) leader said to cheers.

"We must make an effort to make sure that we have the highest turnout... we must confirm a resounding defeat for this regime."

The speech was disrupted at one point when a military helicopter circled overhead.