U.S. President Barack Obama warned of stronger sanctions on North Korea if the North continues provocations.

He held a news conference after holding summit talks with Japanese Prime Minister Yoshihiko Noda at the White House on Monday, local time.

The two leaders agreed to closely cooperate bilaterally and with the international community to address North Korea's provocations, which Obama called a "sign of weakness, not strength."

He said the provocations will only further isolate the communist country.

The U.S. leader mentioned North Korea's "old pattern of provocation that then gets attention and somehow insists on the world purchasing good behavior from them." He said this pattern is broken and the North will be able to gain nothing from further provocative acts.

He said policies that repeat the cycle of provocation and compensation are no longer valid.

On reports of a looming third nuclear test by the North, Obama said he would not predict what might happen in the coming months.