Indian Prime Minister Manmohan Singh is expected to make the trip to Washington for the April 12-13 summit, his office said.

In Pakistan, foreign ministry spokesman Abdul Basit told AFP: "Someone will go to the conference but we don't know the composition of the delegation yet."

The summit's focus is on securing vulnerable nuclear materials and preventing acts of "nuclear terrorism".

India and Pakistan crashed the nuclear club in 1998 by conducting tit-for-tat underground tests.

The tests substantially raised the stakes in the traditional rivalry between the South Asian neighbours, which have fought three wars since independence in 1947 -- two of them over the disputed Himalayan region of Kashmir.

Obama called for a summit, during an April 2009 speech in Prague, when he pledged to work towards a world without nuclear weapons.

More than 40 countries have been invited, though the list of delegates has not been finalised.

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