The U.S. Congress is expected later this week to pass a measure that would freeze up to $700 million in aid to Pakistan because of fears that Islamabad is not doing enough to combat the spread of homemade bombs.
U.S. lawmakers are concerned that militants in Afghanistan are using fertilizer produced in Pakistan to develop improvised explosive devices - one of the militants' most effective weapons against U.S.-led forces there.
State Department spokesperson Victoria Nuland said Tuesday that the proposed suspension would not automatically cut the funding, but will make it dependent on making progress with Pakistan on the issue of homemade bombs.
The aid suspension is part of a larger defense spending bill that U.S. lawmakers are expected to pass later this week.
Several Pakistani officials criticized the move on Tuesday, saying it would only lead to worse relations with Washington.
U.S.-Pakistani ties have suffered since a secret U.S. strike killed al-Qaida leader Osama bin Laden in Pakistan in early May.
Relations reached a new low following a NATO airstrike in November that killed 24 Pakistani troops along the border with Afghanistan.