At a United Nations conference reviewing the nuclear Non-Proliferation Treaty (NPT) Tuesday, the United States said loopholes in the treaty are creating a crisis. A U.S. official told the conference at least four NPT member states have used the treaty as a cover for their efforts to develop nuclear weapons.

U.S. Undersecretary of State for Arms Control John Bolton says there is a broad consensus that steps must be taken to insure full compliance with the treaty by all member states. But he says members have yet to decide how to enforce compliance.

The undersecretary of state says member states such as Iran are actively violating their treaty obligations and have gained access to technologies and materials for their nuclear weapons programs.

Mr. Bolton called Iran "one of the most fundamental challenges to the non-proliferation regime" and said Iran has concealed a "large scale covert nuclear weapons program for 18 years." In comments to the media later, Mr. Bolton said the Security Council must deal with the issue of Iran or risk losing its credibility.

"We have said for over a year that Iran's nuclear weapons program poses a threat to peace and international security. That's the triggering threshold for Security Council jurisdiction. That is why we think it ought to be here. As I said in the speech, if time goes on, and the matter does not get into the Security Council it will undercut not only the NPT, but the Council itself," he said.

The Bush administration has proposed a series of steps to hold nations accountable for secret arms programs. One proposal is that nations developing or trying to acquire nuclear weapons would give up their rights to nuclear technology for peaceful purposes. The proposal would limit the construction of enrichment and reprocessing plants to nations that already possess them.

Mr. Bolton said North Korea is an example of the problem presented by giving members unrestricted access to enrichment and reprocessing technology. North Korea signed the treaty, violated its treaty obligations, and then withdrew. Meanwhile, he said, diplomatic talks aimed at getting North Korea to end its nuclear weapons program in exchange for a guarantee of security are on-going. "If the North Korean enrichment and reprocessing activities are continuing while they stall in these talks, their ability to gather fissile material and perhaps form it into nuclear weapons continues and our diplomatic progress is not sufficient," he said.

Mr. Bolton cited Iraq and Libya as the two other member states that violated the agreement in the past.

According to the NPT, only five nations - Britain, China, France, Russia and the United States - are permitted to have nuclear weapons. It is understood that India, Israel and Pakistan also possess nuclear weapons but they are not signatories to the treaty.