They said Congress would use this assessment to decide whether to continue granting foreign aid to Pakistan.
The letter was signed by Sens. Max Baucus (D-Mont.), Dianne Feinstein (D-Calif.), Robert Menendez (D-N.J.), Ben Nelson (D-Neb.) and Jon Tester (D-Mont.).
"[I]t is incongruous to be providing enormous sums to the Pakistani military unless we are certain that it is meeting its commitment to locate, disrupt and dismantle terrorist threats inside its borders," they wrote.
They asked specifically for an assessment of Pakistan's commitment to end support to extremist groups, preventing them from operating in Pakistan, and strengthening its counterterrorism and anti-money laundering laws.
"We believe that conducting this assessment will be crucial for the Congress to determine whether to provide the full range of security assistance called for in the FY 11 Continuing Resolution and the FY 12 budget," they said.