Islamabad - In a blunt rejection of Pakistan's demand for a civilian nuclear deal as done with India, US President George W Bush said on Saturday that the two countries had different requirements, culture and histories.

After discussions with President Pervez Musharraf, the reporters asked the US leader whether Washington would have with energy-deficient Pakistan a nuclear deal similar to the one that he had reached with Prime Minister Manmohan Singh in New Delhi two days ago.

With Musharraf standing by his side, Bush stated in unambiguous terms that "Pakistan and India are different countries with different needs and histories".

The US President's reference to "different histories" was an obvious reference to the track record of India and Pakistan in the nuclear field. Washington has maintained that India is a responsible nuclear power in contrast to Pakistan's clandestine help in this sphere to some countries highlighted by the actions of its top scientist A Q Khan, now under house arrest.

On Musharraf seeking US involvement in facilitating the resolution of Kashmir and other issues, Bush refused to be drawn into it saying the "best way" for doing so was for leaders of the two countries to "step up and lead".

"The best way for Kashmir to be resolved is for the leaders of both countries to step up and lead, and that's exactly what President Musharraf has done and that's what Prime Minister Singh has assured me he wants to do", he said.

He made it clear that the role of the US was to continue to encourage the parties concerned to come together to resolve the contentious issue.

"The atmosphere is changing," he said noting that the confidence-building measures taken by the two countries have begun to bear fruit. He also referred to India's prompt help to earthquake victims in Pakistan.

Condemning Thursday's suicide attack in Karachi in which an American diplomat was killed, Bush said "we have to fight the war on terror together". Addressing the joint press conference, Musharraf said "I referred to Kashmir and requested him to remain involved for facilitating resolution of all issues including Kashmir to bring peace in the region".

Musharraf said Pakistan and the US have decided to institutionalize their strategic relationship. "We laid the foundations of a strong, sustainable, broadbased long-term relationship. This includes, first of all, commencing the US-Pakistan strategic dialogue in an institutionalized manner," he said.

The dialogue will include defence relations, cooperation against the fight against terrorism and resolution of all disputes in the region including Kashmir, he said.