Indicating that the path to implementation of the Indo-US nuclear deal may not be smooth, Prime Minister Manmohan Singh on Tuesday said there were a 'lot of hurdles' to be crossed.

"We have lot of hurdles to cross. The next stage is NSG (Nuclear Suppliers' Group)," Dr Singh told media persons on the sidelines of a function to launch a book on history, authored by his daughter Upinder Singh, a professor in Delhi University.

New Delhi needs the nod of the NSG and also the approval of the nuclear deal by the US Congress to open the doors of nuclear commerce, ending three decades of isolation.

India expects a 'clean' and 'unconditional' waiver from the NSG to take the deal forward and hopes no new conditions are put that would nullify the safeguards pact.