President Barack Obama's senior foreign policy adviser said Wednesday that the United States is seeking closer security ties with both Japan and South Korea to deal more effectively with aggression by North Korea.

Susan Rice, national security adviser, said in a speech that the United States aims to "deepen trilateral security cooperation and interoperability" with Japan and South Korea.

Obama made trilateral cooperation "a central focus" of his summit with the leaders of Japan and South Korea in March in The Hague and his trip to the region in April, Rice told a think tank conference in Washington.

"In the face of North Korea's increasing provocations, we've developed a tailored deterrence strategy and counter-provocation plan with South Korea," she said.