By FOSTER KLUG, Associated Press Writer Foster Klug, Associated Press Writer – 6 mins ago

WASHINGTON – President Barack Obama said Tuesday that a nuclear-armed North Korea poses a "grave threat" to the world and vowed to end a cycle of allowing Pyongyang to create a crisis and then be rewarded with incentives to back down.

"This is a pattern they've come to expect," Obama said. "We are going to break that pattern."

With South Korean President Lee Myung-bak at his side in the White House Rose Garden, Obama said they agreed that a new U.N. resolution seeking to halt North Korea's development of nuclear weapons and ballistic missiles must be fully enforced. The U.N. did not authorize military force to enforce the measures.

Lee said he and Obama agreed that "under no circumstance are we going to allow North Korea to possess nuclear weapons."

Obama said that North Korea's record of threatening other countries and spreading nuclear technology around the world means it should not be recognized as a legitimate nuclear power.

"We will pursue denuclearization on the Korean peninsula vigorously," Obama said. "So we have not come to a conclusion that North Korea will or should be a nuclear power. Given their past behavior, given the belligerent manner in which they are constantly threatening their neighbors, I don't think there's any question that that would be a destabilizing situation that would be a profound threat not only to United States' security but to world security."

Nor will the international community respond to North Korean provocations, such as additional underground nuclear tests, by offering financial incentives, Lee said.

"They will not be able to gain compensation by provoking a crisis," he said.

North Korea has bargained with other countries for more than a decade about giving up its nuclear program, gaining such concession as energy and economic aid, and then reneging.

Lee also called on the North Korean government to release two American journalists and one South Korean worker who are jailed in the North.

Talk is cheap! Let's see some preemptive nuc-u-lar strikes!