Susan Page, the deputy assistant secretary for African affairs, said the United States was concerned by the recent rise in "political violence, wanton intimidation of the public, and partisan arrests and prosecutions."
She applauded Mugabe’s statement last week calling for an end to the violence but questioned whether that message was filtering down to his security forces.
"We hope President Mugabe, as head of state and commander in chief of the armed forces, also conveys that message to the police and security services," Page said. "The credibility of that statement, however, ultimately will be reflected in if or how it is honoured."
Page said if Mugabe’s party wants to play a constructive role, "it must reject the use of violence and fear in its operations."
Mugabe’s critics accuse the longtime ruler of using violent means to hush his political opponents, who are part of a unity government that Mugabe wants ended.
In recent days, police in Zimbabwe have arrested dozens of political activists, students and trade union members for allegedly plotting an Egyptian-style uprising. Defense attorneys have reported torture of the detainees.
U.S. State Department Spokesman P.J. Crowley said the activists were charged with treason and urged Mugabe’s government to uphold international human rights laws and ensure due process for those arrested.
The United States and the European Union imposed targeted sanctions on Mugabe in 2002.
Mugabe blames those sanctions for his country’s woes — which late last year included a 90% unemployment and an inflation rate of 231,000,000% — and threatened to seize all Western-owned investments in the country unless sanctions were lifted.
Mugabe has held power since Zimbabwe became independent in 1980. In 2009, he formed a coalition government with challenger Morgan Tsvangirai, who was named prime minister.
But last December, Mugabe announced he was tired of working with the opposition party, which he said "lacked ideology and policies" and called for an election this year.
Tsvangirai, however, has threatened to boycott the poll if a referendum on a new constitution is not held.