U.S. Ambassador to the International Atomic Energy Agency Gregory Schulte Wednesday handed over documents to IAEA Director General Mohamed ElBaradei showing the United States had completed ratification procedures. As a result of the completed ratification by the United States, an international nuclear safeguard agreement entered into force, the IAEA reported.

The United States was the last of the world's five formally recognized nuclear-weapon countries to fulfill the nuclear non-proliferation pact obligations.

With the additional protocol entered into force, the IAEA will have greater inspection authority to access nuclear installations and other sites around the world to verify nuclear safeguard agreements.

"A principal aim is to enable the IAEA inspectorate to provide assurance about both declared and possible undeclared activities," the release said.