Zimbabwe's main opposition party says police have arrested one of its newly elected members of parliament.

The Movement for Democratic Change says Heya Shoko was seized Monday in the southern town of Masvingo.

Opposition spokesmen describe the arrest as an attempt to intimidate the party as MDC leader Morgan Tsvangirai prepares for a runoff election against President Robert Mugabe.

The U.S. Assistant Secretary of State for African Affairs, Jendayi Frazer, said in Washington today that for the election to be credible, it would need a massive number of international monitors. She added that Mr. Tsvangirai's security would need to be guaranteed.

Earlier today, Mr. Mugabe's government said it will bar foreign observers from monitoring the vote unless international sanctions on ruling party officials are lifted.

In other news, the pro-opposition Zimbabwe Congress of Trade Unions said today its president, Lovemore Matombo and secretary-general, Wellington Chibebe have been denied bail. The two were arrested last week for making speeches at a workers' day rally.

Rights groups have reported widespread violence and intimidation of opposition activists since the MDC won the March parliamentary elections and Mr. Tsvangirai earned more votes than Mr. Mugabe in the presidential race.

Mr. Tsvangirai says he is the outright winner of the presidential election. But Zimbabwe's electoral commission says he failed to win the majority needed to avoid a second round of voting

A date has not been set for the runoff.