The United States said Friday it had safely transported 68 kilograms of highly enriched uranium -- enough for two nuclear weapons -- from the Czech Republic to Russia.

"The HEU was securely transported to Russia, where it will be downblended into low enriched uranium (LEU) for use in nuclear power reactors," National Security Council spokeswoman Caitlin Hayden said in a statement.

Low-enriched uranium cannot be used for nuclear weapons.

"With this shipment, the Czech Republic becomes the tenth country from which all HEU has been removed since President Obama announced the international effort to secure all vulnerable nuclear material around the world," she added.

US President Barack Obama hosted a 47-nation summit in April 2010 that agreed to a four-year deadline to lock down loose nuclear materials and prevent their falling into the wrong hands.