A Nobel laureate and former nuclear scientist is expressing concern that a new nuclear-arms race may soon be under way.

Mr. Rotblat, 94, was one of the first scientists to work on the development of the atomic bomb in the United States, but he withdrew from the project before the bomb was tested. He has campaigned vigorously against nuclear weapons, and won the Nobel Peace Prize in 1995 for his efforts.

Speaking to reporters in Geneva, Mr. Rotblat said during the Cold War the policy of maintaining nuclear arsenals was justified as a weapon of last resort or to deter other nations from using them. But he says he is alarmed that even though the Cold War has ended work to develop new kinds of nuclear weapons continues.

Mr. Rotblat says scientists in the United States have been developing a so-called mini-nuke, which is a low-yield nuclear weapon able to penetrate underground targets. He said, if the United States decides to test the weapon, other countries are likely to follow suit.

"China would be almost certain to resume testing," he said. "After the U.S. decision to develop ballistic missile defenses, China feels vulnerable, and is likely to attempt to reduce its vulnerability in a modernization and build-up of its nuclear arsenals. Other states with nuclear weapons, such as India or Pakistan, might use the window of opportunity opened by the USA to update their arsenals. The danger of a new nuclear arms race is real."

Mr. Rotblat was in Geneva to receive the 2002 Linus Pauling award for science, peace and health.