The US State Department issued the statement after Mugabe said earlier that Zimbabwe was ready for "fresh and cooperative relations" with Western nations that have spearheaded global condemnation of his rule.
"We encourage Robert Mugabe to show his commitment to positive relations with the US by fully implementing the Global Political Agreement, which he signed in September 2008," State Department spokesman Ian Kelly told AFP.
Mugabe has been accused of blocking attempts to fully implement the terms of the agreement, under which Mugabe continues serving as president and his long-time rival Morgan Tsvangirai took office in February as prime minister.
The unity government is tasked with returning Zimbabwe to stability after years of economic ruin.
Kelly, when asked to comment on Mugabe’s bid to turn the page with the West, said the veteran Zimbabwean leader could "take a number of steps to show a commitment to democratic reform and political opening."
These include "ending politicized arrests and prosecutions and often violent land seizures," he said in an e-mail message.
They also include "replacing the corrupt officials, ending media censorship, and repealing emergency decrees and draconian laws restricting personal freedoms," he added.
He also called on Mugabe to make a public commitment to draft a new constitution and hold national elections under international supervision and monitoring.
In Harare, at the opening session of the new parliament, Mugabe said: "Our country remains in a positive stance to enter into fresh and cooperative relations with all those countries that have been hostile to us in the past."
He said Zimbabwe’s reengagement with the European Union is "gathering momentum," after the EU last month sent a high-level delegation to Zimbabwe to meet with Mugabe and Tsvangirai.
The United States and the European Union have imposed travel restrictions and asset freezes against Mugabe and his key allies.