"Given Mugabe's escalated use of violence, the United States will be imposing additional sanctions against the worst perpetrators of the regime's brutality," said U.S. Assistant Secretary of State for African Affairs Jendayi Frazer.

He said the aim was to turn up the pressure on Mugabe and if the violence by his "tyrannical regime" did not subside, Washington would look at even more punitive measures.

"Mugabe's tyranny needs to end," Frazer said in a speech to the Washington-based Center for Strategic and International Studies.

The United States has already imposed sanctions on about 130 people with ties to Mugabe, and the plan is to expand that list by placing financial restrictions on about half a dozen more people and U.S. travel bans on an additional three dozen.

Frazer cited this year as the worst on record for human rights in Zimbabwe, with about 6,000 instances of abuse recorded and over 90 cases of politically motivated kidnappings and abductions.

In addition, the United States has details of 3,463 victims of torture and assault this year, with victims reporting beatings with whips, cables and electric shocks.

Mugabe, 83, is accused of widespread human rights violations and of cracking down hard on the country's opposition. He has been in power since independence from Britain in 1980.

STUDENT VISAS REVOKED

Included in the three dozen facing orders banning them from traveling to the United States will be nine state security officials who Washington says were involved in rights abuses and "anti-democratic" activities in recent months.

At least five Zimbabweans studying in the United States -- adult children of Zimbabwean government officials implicated in similar "anti-democratic" activities -- will have their U.S. student visas revoked and be forced to leave.

"It is intolerable that those closest to Mugabe are enjoying the privilege of sending their children to the United States for an education, when they have destroyed the once-outstanding educational system in their own country," said Frazer in prepared remarks.

Two companies that are owned or controlled by "specially designated" individuals in Zimbabwe will also be subject to sanctions, making it illegal for U.S. firms to do business with them. Frazer did not name the companies.

Once viewed as southern Africa's bread basket, Zimbabwe's economy is now in ruins and is rated by the World Bank as the fastest shrinking economy outside a war zone.

The country has the world's highest inflation rate, chronic shortages of food, fuel and foreign currency as well as soaring poverty and unemployment.

Mugabe has blamed the economic crisis on sabotage by political opponents. He has strongly criticized U.S. policies toward his country and also lashed out at former colonial ruler Britain.

Britain's Prime Minister Gordon Brown is boycotting a European Union-Africa summit in Lisbon this month in protest against Mugabe's planned presence there. Mugabe is seeking re-election next March, a move strongly opposed by the United States.