U.S. Defense Secretary Robert Gates has named terrorism and the proliferation of weapons of mass destruction as the main threats of the 21st century and mentioned Iran and Hezbollah.

These concerns are especially pertinent with regard to the countries that threaten to destroy other states, Iran for instance, he said answering questions from students of the Kuznetsov Navy Academy in St. Petersburg.

Gates is convinced that the United States, Russia, and China must compel these countries to give up such weapons.

He felt that the world will have to face a whole number of possible conflicts that will be dangerous and deadly to a significant extent.

A threat may come not only from countries but organizations that may have greater possibilities than some states, for instance, Hezbollah has more missiles than some countries do. Terrorist groups must not be allowed to get a hold of weapons of mass destruction, Gates added.

He admitted that after the end of the Cold War the world has become much more complex.

There is more instability, more change; international terrorism and crime are growing, the Pentagon chief said.