Zimbabwe's opposition leader says he is pulling out of Friday's runoff election against President Robert Mugabe.

Morgan Tsvangirai says this is because of mounting violence and intimidation against the opposition during the campaign.

Tsvangirai announced his decision during a news conference in Zimbabwe's capital on Sunday after thousands of ruling party militants blockaded the site of the opposition's main campaign rally.

The opposition says that police in full riot gear and soldiers have taken over the site of the rally.