Discussions are expected to concentrate on nuclear non-proliferation, which has dominated the two countries' relations since Pakistan conducted its nuclear tests in May.

Easing of sanctions

Pakistan has agreed to the US's main demand that it sign the Comprehensive Nuclear Test Ban Treaty (CTBT) next year if economic sanctions are lifted.

President Clinton has already announced a partial easing of the embargo.

But BBC Pakistan Correspondent Owen Bennett-Jones says Pakistan is much more reluctant to give ground in other areas.

In particular, Islamabad is refusing to sign the Nuclear Non-Proliferation Treaty.

Shortly before Mr Sharif's departure, Pakistan's foreign secretary said nuclear deterrence was now an indispensable element of Pakistan's security policy.

Economic reassurance

On his visit, Mr Sharif is also due to discuss economic issues with the World Bank and the International Monetary Fund (IMF), which last week agreed to an economic rescue package for Pakistan.

During negotiations with the IMF, Pakistan gave assurances about its future economic policy.