The US State Department has rejected calls for tighter conditions to be attached to a proposed $3bn American aid package to Pakistan.
The US says its keeping a close eye on Pakistan's nuclear weapons
Opposition Democrats want the aid tied to tighter curbs on Pakistan's nuclear industry after secrets were leaked.
They also wanted the aid package to be tied to political reform and closer co-operation in the "war on terror".
But the State Department said the US continued to monitor Pakistan's nuclear activities following the leaks scandal.
"We don't see any reason - there has been no cause at all for us to have second thoughts about providing any assistance to Pakistan," Christina Rocca, assistant secretary of state for South Asian affairs, told a congressional hearing in Washington.
'Extremely sensitive matter'
Democrat lawmaker Gary Ackerman had warned the hearing that the US had failed to extract sufficient guarantees from Pakistan on the issue of nuclear non-proliferation and democratisation.
"We are hitching our wagon to a very questionable horse," he said.
Pakistani forces often co-ordinate attacks with US troops in Afghanistan
Earlier this year, Pakistan's top nuclear scientist confessed his role in a black-market network which had enabled countries such as North Korea, Iran and Libya to bypass international controls in their pursuit of nuclear weapons technology.
Ms Rocca said the US continued to keep a close eye on Pakistan's nuclear programme.
"We're working very closely with the government of Pakistan on the investigation," she said.
However, she refused to say whether US authorities had independently interviewed the Pakistani scientist at the centre of the nuclear proliferation scandal, Dr AQ Khan, describing it as "an extremely sensitive matter".
US President George W Bush plans to give Pakistan $3bn in aid over five years, starting from 2005.
MAJOR NON-NATO ALLIES
Are eligible for priority delivery of defence material
Can stockpile US military hardware
Can participate in defence research and development programme
Can benefit for a US loan guarantee programme
Earlier in June, he accorded Pakistan the status of a major non-Nato ally, making it one of the few countries - alongside South Korea and Israel - that are entitled to generous deals on US military and financial aid.
The announcement was widely seen as a reward for Pakistani President Pervez Musharraf's co-operation with America's campaign against al-Qaeda and Taleban remnants in the region.
In January, Pakistan received a $400m aid deal from the US.