Obama, S. Korean leader discuss threat from North

Lee secured assurances from Obama that the United States would extend its “nuclear umbrella’’ over South Korea in the face of attacks from the North. In addition, both leaders pledged to pursue a denuclearized Korean Peninsula, with Obama declaring during remarks to reporters that North Korea’s bid to become a nuclear power is not inevitable and will not be accepted by his administration.

“We will pursue denuclearization on the Korean Peninsula vigorously, so we have not come to a conclusion that North Korea will or should be a nuclear power,’’ Obama said. “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 to not only the United States’ security, but to world security.’’

That US pledge of nuclear protection to South Korea has been implicit since the end of the Korean War. But Lee, who has toughened his government’s position toward the North since taking office 16 months ago, came to the United States seeking an explicit White House guarantee.

Lee made the request as the North Korean government prepares to face new UN sanctions, including the searching of its ships on the high seas, and begins an opaque and politically volatile succession process to replace its reportedly ailing leader, Kim Jong Il.

For the Obama administration, which in its first months in office has staked out a pragmatic approach to foreign policy, North Korea has proved to be an issue without an obvious course of action.

Officials, including veterans of the Clinton administration, emphasize that North Korea’s leadership customarily welcomes a new US president with ritual hazing, most recently by brandishing its nuclear weapons program.

Although it first tested a nuclear device in 2006, it was not until this week that the North Korean government publicly acknowledged that it possessed nuclear weapons and intended to make more of them, using its own plutonium and enriched uranium to do so.

Days earlier, the UN Security Council had voted to impose new sanctions on the North Korean government, already struggling with famine on a large scale.

The vote included the support of Russia and China, two veto-wielding members that have defended North Korea in the past. The measures include financial restrictions on the North’s leadership, a ban on its lucrative arms exports, and permission for countries to search North Korean ships at sea.

The Obama administration, as well as other Security Council members, fears the possibility of North Korea exporting its nuclear technology. But the North Korean government has warned that it would consider the boarding of its vessels an act of war.

The sanctions were a response to North Korea’s recent tests of short- and long-range missiles, and more seriously, a more powerful nuclear device than the one detonated three years ago.