The Bush administration came under attack over Pakistan's nuclear reactor programme with some lawmakers accusing it of withholding the information from the US Congress at a time when important policies with respect to India and Pakistan were being debated.

Gary Ackerman, a key lawmaker, demanded that the administration should stop its plan to sell F-16 fighter jets to Pakistan, saying their acquisition plus the plutonium reactor being built by Islamabad equals a "catastrophe."

"At any time this news (about Pakistan building a plutonium reactor at its Khushab nuclear plant) would be unwelcome," Ackerman, the Co-Chair of the Congressional Caucus on India and Indian Americans, said in a "Dear Colleague" letter.

The import of the story is "truly alarming" in the context of a pending sale by US of F-16 fighter-bombers, he said pointing to The Washington Post piece about the dramatic expansion in Pakistan's nuclear weapons programme.

Despite assurances by the Bush Administration that these aircraft would not be misused or their technology transferred to other countries like China, "once these planes have been delivered to Pakistan, there is, in fact, absolutely nothing we can do to prevent misuse," the Democrat said in his letter.

"Based on history and strategic analysis, there is every reason to believe the contrary that these F-16s will be drafted for use as nuclear weapons delivery vehicles, and that they will be picked apart by potential adversaries to answer questions about our aviation capabilities."

"Help stop a catastrophe before it happens... and stop the sale of F-16s to Pakistan" the lawmaker, said.

Democratic Congressman Edward Markey also attacked the administration over the Pakistan reactor and said it could ignite a nuclear arms race in South Asia. "...Instead of doing everything possible to stop this vicious cycle, the Bush Administration is throwing fuel on the fire. If either India or Pakistan starts increasing its nuclear arsenal, the other side will respond in kind; and the Bush Administration's proposed nuclear deal with India is making that much more likely" Markey, a longtime critic of the Indo-US nuclear deal said in a statement.

The lawmaker was one of the first to oppose the deal and is expected to rally support for his efforts on the floor on Wednesday. "Both Pakistan and India need to reverse their decisions to increase their nuclear arsenals, and take a step back from the brink.

"And President George W Bush [Images] should seize the opportunity that this calm before the storm represents to take bold leadership on negotiating a verifiable treaty which would permanently cap global bomb-making material stockpiles," he said.

Bush also needs to press both India and Pakistan to agree to suspend production of bomb-grade fissile materials while such a cut-off treaty is being negotiated" the lawmaker added. The US had on Monday said that was aware of Pakistan's plans for some time but discourages military use of the facility.