US Deputy Secretary of State John Negroponte - who is in Pakistan - has spoken on the telephone to opposition leader Benazir Bhutto.
Some opposition supporters do not welcome Mr Negroponte's visit
He told her "moderate forces" should work together to get Pakistan back to democracy, the State Department said.
The conversation took place after Ms Bhutto was freed from house arrest.
The former PM renewed her calls for President Pervez Musharraf to end emergency rule, and condemned the interim government overseeing polls.
Ms Bhutto was placed under house arrest in Lahore on Tuesday to stop her from leading a march to Islamabad.
The move was part of a huge clampdown that has seen thousands of people arrested since emergency rule was introduced on 3 November.
Mr Negroponte is in Islamabad for talks with the government. It is not clear if he will meet opposition leaders.
Washington had been hoping for Ms Bhutto and Gen Musharraf to work together to give his government more support in its fight against pro-Taleban extremists.
But after her release, Ms Bhutto dismissed the interim government sworn in on Friday: "This caretaker government is an extension of the (governing PML-Q party) and is not acceptable."
And she again appeared to rule out resuming talks on a power-sharing deal with Gen Musharraf.
"I can't see how I can team up with somebody who raises hopes and dashes them... He talked to me about a roadmap to democracy and imposed martial law," she said.
Ms Bhutto says she will meet other opposition leaders soon to discuss a boycott of January's assembly elections.
'I take pride'
Gen Musharraf meanwhile praised the outgoing government after its term expired on Thursday.
"I take pride in the fact that, being a man in uniform, I have actually introduced the essence of democracy in Pakistan, whether anyone believes it or not," he said, after the interim government was sworn in.
The US administration has made repeated calls for the emergency to be lifted and for Gen Musharraf to become a civilian leader.
Benazir Bhutto was placed under house arrest on Tuesday
Gen Musharraf says he will resign as head of the army once the Supreme Court has ratified his next term as president.
He sacked a number of Supreme Court judges who had been due to rule on whether he could be president for a second term.
Correspondents say the replacement judges are expected to rule that his election last month was legal.
Apart from Ms Bhutto, some other leading figures were released from detention on Friday.
They include the country's most prominent rights activist, Asma Jahangir, head of the Human Rights Commission of Pakistan.