The chief security advisor to South Korea's president says Seoul and Beijing have agreed to cooperate to try to prevent North Korea from conducting a nuclear weapons test.

Song Min-soon said late Friday if North Korea carried out a nuclear test, it would create a situation more grave than its test-firing of missiles last month. He said South Korea and China plan to prevent that from happening. Song, who did not elaborate, returned from a two-day visit to Beijing on Friday.

North Korea test-fired seven missiles July 5, and a recent U.S. media report on ABC News said the country may be preparing to test nuclear weapons underground.

Diplomatic efforts to lure North Korea back to multilateral nuclear talks have intensified over the past month. But South Korea's foreign minister Ban Ki-moon says the chances of resuming the talks have declined.

South Korea is urging the international community to take a firm stance against North Korea's nuclear ambitions, but has cautioned against pressing the reclusive state too hard on the issue.

Japan's chief Cabinet secretary Shinzo Abe says any tests of nuclear weapons by North Korea would be a totally unacceptable threat to Northeast Asia.