In what would be the first test for the new U.N. sanctions against the North, South Korean media also reported Sunday that a North Korean ship sailing toward Myanmar via Singapore was being shadowed by the U.S. military over suspicion that it may be carrying illicit weapons.
U.S. officials said Thursday that the U.S. military had begun tracking the ship, Kang Nam, which left a North Korean port Wednesday.
South Korean television network YTN, citing an unidentified intelligence source in the South, reported that the U.S. suspected the 2,000-ton-class ship was carrying missiles and other related weapons toward Myanmar — which has faced an arms embargo from the United States and the European Union and has reportedly bought weapons from North Korea.
The report said the U.S. has also deployed a navy destroyer and has been using satellites to track the ship.
South Korea's Defense Ministry, Unification Ministry and the National Intelligence Service said they could not confirm the report.
Tension on the Korean peninsula has spiked since the North defiantly conducted its second nuclear test on May 25. North Korea later declared it would bolster its atomic bomb-making program and threatened war in protest of U.N. sanctions for its test.
Obama reaffirmed Washington's security commitment to South Korea, including through U.S. nuclear protection, after a meeting Tuesday in Washington with South Korean President Lee Myung-bak. Obama also said the U.N. sanctions will be aggressively enforced.
In its first response to the summit, North Korea's government-run weekly Tongil Sinbo said that Obama's comments only revealed a U.S. plot to invade the North with nuclear weapons.
"It's not a coincidence at all for the U.S. to have brought numerous nuclear weapons into South Korea and other adjacent sites, staging various massive war drills opposing North Korea every day and watching for a chance for an invasion," said the commentary published Saturday.
The weekly also said the North will also "surely judge" the Lee government for participating in a U.S.-led international campaign to "stifle" the North.
North Korea says its nuclear program is a deterrent against the U.S., which it routinely accuses of plotting to topple its communist regime. Washington, which has 28,500 troops in South Korea, has repeatedly said it has no such intention and has no nuclear weapons deployed there.
On Saturday, a South Korean Foreign Ministry official said Seoul has proposed five-way talks with the U.S., China, Russia and Japan to find a new way to deal with the North's threats.
The U.S. and Japan have agreed to participate, while China and Russia have yet to respond, the official told The Associated Press, requesting anonymity because he was discussing a plan still in the works.
North Korea and the five countries began negotiating under the so-called "six-party talks" in 2003 with the aim of giving the communist regime economic aid and other concessions in exchange for dismantling its nuclear program. In April, however, the North said it was pulling out of the talks in response to international criticism of its controversial April 5 long-range rocket launch.