Obama's meeting with Lee, set for later in the day, is expected to focus on the North's plan to launch a long-range rocket next month to put what it claimed is a satellite into orbit, a pretext the unpredictable regime has long used for banned missile tests.

The North's announcement has sparked strong international denunciations as it came just weeks after Pyongyang reached a rare deal with Washington under which the country agreed to put a moratorium on nuclear and missile tests, freeze uranium enrichment and accept U.N. nuclear monitors in return for 240,000 tons of food aid.

The U.S. has said the planned liftoff, if pushed ahead, would be a deal breaker.

North Korea claims that it has a sovereign and legitimate right to launch a satellite and its "space" program has nothing to do with the deal with the U.S. On Friday, Pyongyang said the launch plan has entered "a full-fledged stage of action."

The North also warned it will take "strongest countermeasures which no one can imagine" if South Korea "dares find fault with its nuclear deterrent and satellite launch and kick off" an anti-Pyongyang racket at next week's Nuclear Security Summit in Seoul.

Obama's three-day trip to South Korea, his third, also includes a visit to the Demilitarized Zone on the border with North Korea, a move believed to be designed to underscore Washington's commitment to defend the Asian ally.

About 28,500 U.S. troops are stationed in South Korea, a legacy of the 1950-53 Korean War.

The Lee-Obama meeting on Sunday is the first between them since December's death of North Korean leader Kim Jong-il. The late leader's youngest son, Jong-un, took over power in the North.

Lee and Obama are expected to reaffirm that the planned rocket launch is a grave provocation that violates a U.N. Security Council resolution banning the communist nation from any ballistic missile activity.

The two leaders are scheduled to hold a joint news conference after the summit.

On Monday, Obama plans to deliver a speech to college students before attending the two-day Nuclear Security Summit, a biennial conference that was established under his initiative to make the world safer without nuclear weapons. The inaugural summit was held in Washington in 2010.

North Korea has denounced the Seoul security summit as an attempt to put pressure on it to give up its nuclear programs. The country has warned that if the Seoul summit produces any statement critical of its planned rocket launch, it will consider it a "declaration of war."

The North's missile program has long been a regional security concern, along with its nuclear programs. The country is believed to have advanced ballistic missile technology, though it is still not clear whether it has mastered the technology to put a nuclear warhead on a missile.

Pyongyang carried out two nuclear tests, first in 2006 and then in 2009. (Yonhap News)