The Zimbabwean government has delayed the country's run-off presidential election until as late as July.

Officials say they have delayed second-round voting by at least 21 days and as much as 90 days after the May second announcement of first round voting results.

A spokesman for the opposition Movement for Democratic Change (MDC) condemned the government's decision Wednesday to delay the vote, saying it was illegal.

The MDC took control of parliament in the March elections, and claims to have won an outright victory in the presidential poll. The official tally shows MDC leader Morgan Tsvangirai falling short of the majority needed to avoid a second round.

The United States called on Zimbabwe's government Wednesday to set a firm date for the election and to take steps to assure the integrity of the process.

In another development, U.S. State Department spokesman Tom Casey said Wednesday the United States has filed an official protest over what he called harassment by Zimbabwean police against U.S. Ambassador James McGee and other foreign diplomats.

In two incidents Tuesday, police stopped and subjected McGee and several colleagues to lengthy questioning after they had visited a hospital that is treating victims of recent post-election violence.

A U.N. official warned Tuesday that post-election violence in Zimbabwe is rising to near-crisis levels. The U.N. representative in Zimbabwe, Agustino Zacarias, told reporters there is an emerging pattern of violence mainly targeting rural supporters of the MDC.

The U.S. State Department Wednesday renewed an advisory for U.S. citizens to defer non-essential travel to Zimbabwe. It said Zimbabwean security forces are creating what it called a "climate of intimidation and fear" ahead of the run-off election.

Some information for this report was provided by AFP, AP and Reuters.