United States has stepped up diplomatic efforts to defuse the deepening political crisis in Pakistan, with Special Envoy Richard Holbrooke asking the country's top leadership to resolve differences with the PML-N so that they could focus on the war against militancy.

Holbrooke, the Special Envoy for Pakistan and Afghanistan, spoke to both President Asif Ali Zardari [Images] and Prime Minister Yousuf Raza Gilani [Images] on telephone to discuss the prevailing situation in the country.

Official sources were quoted by television news channels as saying that Holbrooke had expressed concern over the political crisis during his conversation with Zardari. He called for the resumption of dialogue to end the crisis, the sources said.

While assuring the full support of the US for the continuation of the democratic process in Pakistan, Holbrooke said political stability in the country was imperative to fight militancy effectively, the sources added.

Zardari said the ruling Pakistan People's Party is following the democratic path and showing flexibility while the other parties were non-cooperative.

An official statement issued by presidential spokesman Farhatullah Babar said there was a triangular telephonic conference tonight between Zardari, Holbrooke and US Ambassador [Images] Anne Petterson.

"A host of issues of mutual interest to both Pakistan and the US came under discussion in the teleconference that lasted for about 30 minutes," the statement said.

A separate statement issued by Babar said British Foreign Secretary David Miliband too telephoned Zardari to discuss a "host of issues of mutual interest".

The Prime Minister's House issued a release that said Holbrooke called Gilani and discussed "matters of mutual interest".