Washington, Dec 13 (IANS): In the midst of a tense standoff with Islamabad, a Congressional panel has agreed to freeze $700 million in US aid to Pakistan unless it helps in the fight against homemade bombs in Afghanistan.

The freeze on US aid was agreed to by leaders of the armed services committees from both Republican and Democratic parties in the House and Senate as part of a defence bill that is expected to be passed this week.

The US wants "assurances that Pakistan is countering improvised explosive devices in their country that are targeting our coalition forces", Republican House Representative Howard McKeon told reporters Monday.

He said the bill would also require the Pentagon to deliver a strategy for improving the effectiveness of US aid to Pakistan, which has received some $20 billion in security and economic aid from the US since 2001.

Militants use improvised explosive devices as the most effective weapons against US and coalition troops in Afghanistan. Many are made using ammonium nitrate, a common fertiliser shipped across the border from Pakistan.

"The vast majority of the material used to make improvised explosive devices used against US forces in Afghanistan originates from two fertilizer factories inside Pakistan," Senator John McCain, 2008 Republican presidential candidate, said last week.

The freeze agreement comes amid the worsening of US-Pakistan relations over a Nov 26 NATO airstrike killing 24 Pakistani soldiers near the Pakistan-Afghanistan border.

US relations with the key ally have been strained since the May 2 US raid in which Al Qaeda leader Osama bin Laden was killed in his hideout in the military town of Abbottabad near Islamabad.