Speaking on the sidelines of Nuclear Security Summit, Obama said the US was working through legal processes for giving India access to Headley.
Briefing to reporters, Foreign Secretary Nirupama Rao said the Prime Minister took up the issue of Headley, the activities of LeT and its founder-ideologue Hafiz Saeed, the suspected mastermind of the Mumbai attacks.
"He (Obama) was fully supportive of our request for provision of such access," Rao said.
Manmohan Singh said, "Terrorist onslaught in our region, if it persisted, could affect our growth prospects."
Singh also pointed out that terrorism "was an issue on which India and the US stood on the same side."
"Unfortunately, there was no will on the part of Pakistan to punish those responsible for the terrorist attacks in Mumbai," Rao quoted Manmohan Singh telling Obama.
Obama also assured him that the aid to Pakistan would be monitored and kept under observation keeping India's interests in mind, Rao added.