The US Defense Department has a $three billion plan to train and equip Pakistan's military over the next five years, US media reported on Friday.
The funds would pay for helicopters, night-vision goggles and other equipment and counterinsurgency training for Pakistan's special operations forces and Frontier Corps paramilitary troops, the New York Times said.
It quoted Pentagon officials as saying up to $500 million could come from a yearly emergency war budget that President Barack Obama's administration is to present to Congress next week.
But with some legislators expressing concern over the Pakistan Counterinsurgency Capability Fund, the top US military officer acknowledged that the United States had not mandated enough accountability for the funds.
"There hasn't been an audit trail, and there haven't been accountability measures put in place, and there needs to be for all the funds," Admiral Mike Mullen, the chairman of the Joint Chiefs of Staff, told the Times's editorial board.
"So we're going to do that. For this counterinsurgency money, which is important, it is critical that it goes for exactly that and nowhere else."
Mullen said the Pakistani military must change its focus from fighting arch-foe India to combating militants and insurgents within its borders. "That's not going to change overnight," he said.
Mullen said insurgents operating in safe havens in Pakistan were preparing attacks against Afghanistan and Pakistan.
"The Taliban, in particular, are going both ways now," he said. "They are coming toward Islamabad and they are actually going toward Kabul. I'm completely convinced that the vast majority of the leaders in Pakistan understand the seriousness of the threat."
With insurgents in Afghanistan led and backed by hardline militants in tribal areas over the border in Pakistan, the United States has warned Islamabad that in return for economic and military aid it must crack down on Islamist groups.
Mullen said last month that aid to Pakistan needed to be linked to concrete action but expressed confidence that the country's military grasped the nature of the threat within its borders.
He said the Pakistani military leadership, including chief of staff General Ashfaq Kayani, understood that the militants posed a threat to Pakistan itself.
"I have great confidence in General Kayani and in the Pakistani military," said Mullen, who holds frequent talks with his Pakistani counterpart.
Despite the deployment of more than 100,000 troops, Pakistan has been unable to stop a wave of attacks by Taliban and Al-Qaeda-linked militants that have killed 1,700 since July 2007.