The US Defence Secretary Robert Gates has said that any new government in Pakistan should be wary of holding talks with pro-Taleban insurgents.
Pakistani forces have been battling militants near Afghanistan
Mr Gates told the BBC the previous administration's efforts to negotiate with the militants had not worked out.
Opposition parties are uniting to form Pakistan's next government after faring well in last week's polls. President Pervez Musharraf's allies fared poorly.
Speaking in Delhi, Mr Gates said the polls had been bad for Mr Musharraf.
But Mr Gates said the US hoped to continue working with the man he described as the elected president of Pakistan.
President Musharraf was re-elected to the presidency last year in a parliamentary vote boycotted by opposition parties as unconstitutional.
The former general has been a key US ally in the "war on terror" but his domestic popularity has plummeted amid accusations of incompetence and authoritarianism.
The army has been locked in a faltering campaign against Islamist pro-Taleban militants based along Pakistan's border with Afghanistan, particularly in the Waziristan region.
Mr Gates said a new government would have to face the reality that al-Qaeda militants and insurgents were operating along the frontier.
"Even the Musharraf government tried talking and doing deals in Waziristan. That didn't work out very well," he said.
"Maybe this new government in Pakistan will have to go through the same experience itself."
Opposition leaders have hinted they are willing to talk to the insurgents, with a view to drawing them into the political process.
Meanwhile, the opposition parties hoping to form Pakistan's next government have urged President Musharraf to approve a new parliament.
The call was made in Islamabad at a gathering of opposition MPs, billed as a show of force.
A spokesman for the Pakistan People's Party (PPP), which won the most seats in the elections, said the meeting was "a public demonstration of the strength of the democratic forces in the parliament and their determination to push ahead with their agenda".
Mr Zardari (left) and Mr Sharif must yet agree details of the coalition
Farhatullah Babar told the Associated Press news agency that parliament ought be convened in early March.
"There is no escape from it. I don't think Musharraf can in any way delay that."
The PPP and its chief coalition ally, the PML-N, are trying to attract independent MPs in an effort to secure a two-thirds majority in parliament.
Such a majority would increase their leverage over President Musharraf - though it is unclear if they will seek to oust him.
Both main opposition parties - until recently, bitter rivals - are associated with former prime ministers of Pakistan.
The PPP is led by Asif Ali Zardari, the widower of former PM Benazir Bhutto, who was assassinated in December.
The PML-N is led by Nawaz Sharif, who led the country until he was ousted in 1999 in a military coup engineered by the then-Gen Musharraf.