A South Korean news agency reports that North Korea says it has boosted its nuclear weapons arsenal to protect itself from the United States.

The Yonhap news agency said North Korea's state radio claimed Pyongyang has increased its weapons arsenal in the event of a preemptive U.S. attack.

The report comes as the United States and South Korea are in carrying out joint military exercises.

It also follows a statement by U.S. Secretary of State Condoleeza Rice that Washington is considering "other options" if North Korea does not return to the six-nation talks on its nuclear weapons program.

Ms. Rice did not specify what actions are being looked at. But after meeting with China's foreign minister in Beijing today (Monday), she said there are other options in the international system.