A court in Zimbabwe has released 14 opposition activists charged with committing political violence.

The opposition Movement for Democratic Change (MDC) says in a statement Tuesday that the activists were freed Monday after the state failed to produce its key witness, a police officer who died earlier in the day.

The MDC says more than 1,000 other activists and officials remain in jail on what it termed "trumped up" charges of political violence. The MDC is insisting on their release as a condition for negotiations with the government.

Meanwhile, U.S. President George Bush says the United States is looking at ways to punish Zimbabwe's leaders after U.S.-proposed sanctions were blocked at the United Nations last week.

Mr. Bush says that he was displeased with China and Russia for blocking the measure. He says that the U.S. State and Treasury departments are now working on potential U.S. action.

Earlier Tuesday, U.S. Secretary of State Condoleezza Rice slammed the governance of Zimbabwe's President Robert Mugabe - saying what she called the "heartbreaking plight of  the Zimbabwean people" is one of Africa's major challenges.

Also, the heads of Zimbabwe's Christian churches issued a joint statement expressing concern over the deteriorating situation in the country.

Both Zimbabwe's government and the opposition have been under international pressure to enter talks since the re-election of Mr. Mugabe last month in a widely-condemned runoff vote in which he was the only candidate.

MDC leader Morgan Tsvangirai dropped out a few days before the election after many of his supporters were killed in violence he said was state-sponsored.

Some information for this report was provided by AP.