U.N. Secretary-General Kofi Annan says the world may soon face what he calls a "cascade" of countries acquiring nuclear weapons.

Mr. Annan says relying on the Nuclear Non-Proliferation Treaty is not enough and proposes new, joint action, including tougher inspection rules.

His comments at a security conference in Germany Sunday come as concerns grow over North Korea and Iran's nuclear programs.

German Foreign Minister Joschka Fischer struck a tougher tone on Iran, telling the conference Tehran could be referred to the U.N. Security Council if it resumes nuclear enrichment activities.

Germany, France and Britain have been leading diplomatic efforts to persuade Iran to not develop nuclear weapons, which Tehran says it is not trying to do.

The United States has called for a tougher line with the country

Some information for this report provided by AP and Reuters.