Prime Minister Manmohan Singh [Images] is expected to brief United States President George W Bush [Images] on the developments about the India-United States nuclear agreement in the wake of stiff opposition by the Left parties.

In his telephonic conversation, Singh is likely to apprise Bush about the hurdles faced by his government in taking the next steps to operationalise the deal.

India has to reach a safeguards agreement with the International Atomic Energy Agency and secure changes in the guidelines of the 45-member Nuclear Suppliers' Group to allow nuclear commerce with it.

The Left parties have repeatedly threatened of grave consequences for the Congress-led United Progressive Alliance if it goes ahead with the operatinalisation of the deal.