SEOUL, Republic of Korea - The Democratic People's Republic's Korea (DPRK) warned Wednesday of a "thousand-fold" military retaliation against the US and its allies if provoked, the latest threat in its drumbeat of rhetoric in defense of its nuclear program.

The warning, carried by the DPRK's state media, came hours after US President Barack Obama declared it a "grave threat" to the world and pledged that new UN sanctions will be aggressively enforced.

US President Barack Obama speaks as South Korean President Lee Myung-bak (L) listens during a joint news conference in the Rose Garden of the White House in Washington after their meeting in the Oval Office June 16, 2009. [Agencies]

Obama and President of the Republic of Korea (ROK) Lee Myung-bak met in Washington on Tuesday for a landmark summit in which they agreed to build a regional and global "strategic alliance" to persuade the DPRK to dismantle all its nuclear weapons.

Pyongyang claims its nuclear bombs are a deterrence against the United States and accuses Washington of plotting with Seoul to topple the DPRK, led by Kim Jong Il, who is reportedly preparing to hand over power to his 26-year-old youngest son.

"If the US and its followers infringe upon our republic's sovereignty even a bit, our military and people will launch a one hundred- or one thousand-fold retaliation with merciless military strike," the government-run Minju Joson newspaper said in a commentary.

The commentary, carried by the official Korean Central News Agency, also called Obama "a hypocrite" for advocating a nuclear-free world while making "frantic efforts" to develop new nuclear weapons at home.

"The nuclear program is not the monopoly of only the US," it said.

Rodong Sinmun, another state-owned newspaper, accused the US of deploying new weapons in the ROK and other neighboring countries to invade the DPRK.

"The acute situation on the Korean peninsula is calling on our military and people to further bolster our war deterrence with the high-profile national awakening," said the Rodong Sinmun commentary, also carried by KCNA.

Attention has been focused on the DPRK since it conducted a nuclear test - its second - on May 25 in defiance of the United Nations. The UN Security Council responded by toughening an arms embargo against the DPRK and authorizing ship searches in an attempt to thwart its nuclear and ballistic missile programs.

The UN, however, did not authorize military force to enforce the measures.

The DPRK, which conducted its first test in 2006, is believed to have enough weaponized plutonium for at least half a dozen atomic bombs. It revealed last week that it is also producing enriched uranium. The two materials are key ingredients for making atomic bombs.

The nuclear test - amid suspicion that is preparing for a third one - has effectively brought to a halt the six-party talks aimed at giving the DPRK fuel and other benefits in exchange for dismantling its nuclear program. The talks involved the DPRK, the ROK, China, the US, Japan and Russia.

Obama said the world must break a pattern in which the DPRK puts the world on edge with its threats, only to secure more concessions by promising to reduce tensions.

He said the US is more than willing to negotiate with the DPRK to bring peace on the Korean peninsula.

"But belligerent, provocative behavior that threatens neighbors will be met with significant and serious enforcement of sanctions that are in place," he said.

Lee said his country's alliance with the US will "prevent anything from happening."

Pentagon officials warned Tuesday that the DPRK's missiles could strike the US within three years if its weapons growth goes unchecked.