President Bush and Russian President Vladimir Putin have announced the creation of the Global Initiative to Combat Nuclear Terrorism.
In a joint statement on Saturday, the leaders called nuclear terrorism one of the world's most pressing security challenges.
The U.S. and Russia are calling on other countries to further develop partnerships to combat nuclear threats.
The joint statement says participating countries will work with the International Atomic Energy Agency to ensure the proper control over and protection of nuclear materials. They also will take steps to ensure the safety of nuclear facilities, and to deny safe haven and prosecute terrorists.
The two countries stress that such efforts will be carried out in accordance with international law.
President Bush and President Putin also announced a decision to begin talks on an agreement on cooperation in the peaceful civilian use of nuclear energy.