The US has linked several plots of attacks on its soil to networks in Pakistan, including the May attempt to bomb Times Square in New York.
Rand said Pakistani leaders continue to provide support to some groups.
It said the country's acquisition of nuclear weapons "emboldened its support to militant groups by dampening concerns of retaliation by India".
However, the policy backfired after the attacks in the US on September 11, 2001, when groups including the Pakistani Taliban started a bloody campaign in Pakistan.
Last week, a report by the London School of Economics claimed that Pakistan's intelligence service has a direct link with the Taliban in Afghanistan.
"Pakistan has long used support of militant groups as a foreign policy tool."
Seth G Jones, Rand researcher
The report said Pakistan's Inter-Services Intelligence agency (ISI) provides funding and training for the Taliban, and that the agency has representatives on the so-called Quetta Shura, the Taliban's leadership council, which is believed to meet in Pakistan.
"Pakistan has long used its support of militant groups as a foreign policy tool, so ending that will take time," Jones said.
"US leaders need to work with Pakistan on a timeline with measurable benchmarks for success, as well as the establishment of an enforcement mechanism through intelligence collection.
"Military aid should be conditioned on success in meeting these objectives."
The Rand study further concluded that the US should lessen its reliance on Pakistan where it can.
One area where alternatives can be sought is the use of Pakistan as a route for supplies to the foreign forces in Afghanistan.
Nato transports nearly 50 per cent of its supplies through Pakistan from the port city of Karachi and lorries carrying goods are attacked regularly.
Rand said alternatives land routes could be through Iran and Central Asia.