Conditions for a free and fair election are being undermined by the Zimbabwe government

Ari Fleischer, White House spokesman

The ban will also include people who, through their business dealings, benefit from the policies of the government in Harare.

White House spokesman Ari Fleischer said the action was being taken because "conditions for a transparent election process in Zimbabwe have eroded".

The European Union has already imposed a travel ban on Zimbabwe's political leaders, and announced a freeze on any assets they hold in the EU, following the expulsion of its chief elections observer from Zimbabwe last weekend.

Press restrictions

The order to impose the travel ban came from President George Bush as concern in Washington grows that rising political violence in Zimbabwe and curbs on press freedom are threatening the chances of a free election.

Mr Mugabe is already subject to EU sanctions

Mr Fleischer said the expulsion of Pierre Schori, head of the EU election observer mission, was an indication that "conditions for a free and fair election are being undermined by the Zimbabwe Government".

The BBC's Washington correspondent Rob Watson says that, although the US is allowing the EU to take the lead on Zimbabwe sanctions, it clearly supports their line.

Tension is rising in Zimbabwe ahead of the 9-10 March ballot, which presents Mr Mugabe with his toughest test in 22 years of power.

Observers attacked

On Friday the offices of the opposition party, Movement for Democratic Change (MDC), in the central town of Kwekwe was attacked by suspected pro-government militants while two members of South Africa's elections observation team were inside.

The EU team pulled out last week

About 200 youths threw stones, smashing office windows and damaging the observers' car, Samuel Motsuenyane, the head of the South African delegation said.

Mr Motsuenyane said that the attack was clearly politically motivated, but that his team of observers would not be deterred.

South Africa and the 14-member Southern African Development Community have the largest number of foreign observers in Zimbabwe since the EU pulled out earlier this week.

Gunfire

There were reports of violence elsewhere on Friday.

The opposition said police fired twice on a convoy of vehicles carrying its presidential candidate, Morgan Tsvangirai, and party officials. No one was injured.

Opposition spokesmen also said police used tear-gas to break up a rally south of the capital Harare after claiming there had been no authorisation for the gathering.

The US Government urged Zimbabweans to break the cycle of violence, but stopped short of telling them to vote against Mr Mugabe.

"There is still time for the Zimbabwe Government to reverse this process before 9 March to allow for a legitimate vote," Mr Fleischer said.

"President Bush hopes that soon the people of Zimbabwe again will enjoy political and economic freedoms."