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.

“We have not cut 700 million [U.S. dollars] in aid to Pakistan. What we have is something on the defense authorization bill, which is currently moving in the Congress, which would require the Department of Defense to continue providing a strategy on how we will use certain military systems and measure its progress, in particular, on progress that we are making on the IED issue.”

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.

In response to the airstrike, Islamabad ordered the United States to vacate a Pakistan airbase and has indefinitely closed the two main overland routes NATO uses to send supplies to Afghanistan.

But the top U.S. commander in Afghanistan, General John Allen, said Tuesday that he achieved progress during talks with Pakistan on rebuilding cross-border security cooperation after the incident.

“I do have a sense of progress, and, in fact, I have had a conversation with [Pakistani] General [Ashfaq Pervez] Kayani. The intent of the conversation, the outcome of the conversation, was that we stated our mutual commitment to address any shortfalls that might have caused this event, but also to ensure that we work closely together, because the border is always going to be there.”

Allen said he spoke on the phone Monday with Pakistan's army chief Ashfaq Pervez Kayani.

Many in the U.S. have become increasingly frustrated with what they see as Islamabad's lack of cooperation in fighting Pakistani-based militant groups who attack U.S. forces in Afghanistan.

Earlier this year, the U.S. suspended $800 million of the $2.7 billion in annual military aid it gives to Pakistan.