MOSCOW -- Russia and China urged North Korea on Wednesday to return to the negotiating table on the fate of its rogue nuclear programs -- an unusual joint appeal from two Security Council members who have resisted more punitive U.S. measures against Pyongyang.
The appeal, which also expressed "serious concern" about tensions on Korean peninsula, came just hours after North Korea warned of a "thousand-fold" military retaliation against the U.S. and its allies if provoked. The United States, meanwhile, called on Pyongyang to stop its saber-rattling and negotiate.
The fact that the Chinese and Russian leaders used their meetings in Moscow to jointly pressure North Korea appeared to be a signal that Moscow and Beijing are growing impatient with Pyongyang's stubbornness. Northeastern China and Russia's Far East both border North Korea and Pyongyang's unpredictable actions have raised concern in both countries.
And with both Washington and Pyongyang exchanging near daily rhetorical salvos, Russia and China appeared to be positioning themselves as moderators in the dispute.
After meetings at the Kremlin, Chinese President Hu Jintao joined Russian President Dmitry Medvedev in urging a peaceful resolution of the Korean standoff and the "swiftest renewal" of the now-frozen talks involving their countries as well as North and South Korea, Japan and the United States.
"Russia and China are ready to foster the lowering of tension in Northeast Asia and call for the continuation of efforts by all sides to resolve disagreements through peaceful means, through dialogue and consultations," the statement said.
The comments -- contained in a lengthy statement that discussed a host of other global issues -- included no new initiatives, but it appeared to be carefully worded to avoid provoking Pyongyang. In remarks after their meetings, Medvedev made only a brief reference to North Korea and Hu did not mention it.
Hours earlier, North Korea reacted angrily to President Obama's declaration that North Korea was a "grave threat" to the world. Obama spoke during a summit with South Korean President Lee Myung-bak in Washington.
"If the U.S. 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.
Both China and Russia long resisted efforts by Washington to impose stricter sanctions or other punitive measures on North Korea. But after North Korea conducted a second nuclear test May 25 in defiance of the United Nations, Beijing and Moscow joined with the United States and other Security Council members in passing new tough sanctions.
Those measures include an expanded arms embargo, authorizing ship searches if there are reasonable grounds to suspect the vessels are carrying banned weapons and material to make nuclear weapons and ballistic missiles, and urging all countries and financial institutions to stop financing North Korea's nuclear program.
China's enforcement of the sanctions is seen as crucial. Still, critics say the measures will not stop North Korea from trying to trade weapons with rogue nations or bite too deeply into its already crumbling economy.
Moscow was one of North Korea's strongest backers during the Cold War, providing Pyongyang with military and economic aid for years. Those ties withered after the 1991 Soviet collapse, leaving China as the only country with any real clout with Pyongyang.
In recent years, however, Moscow has sought to re-nurture those relations with the reclusive regime.
Russia has said North Korea is not solely to blame for the breakdown of the six-nation talks, suggesting the United States, South Korea and Japan also must share responsibility.
Japanese and South Korean news reports said North Korea was preparing another site to test-fire a missile that experts say could be capable of striking the United States.
In Vienna, senior delegates of the U.S. and other countries discussed the situation Wednesday with the 35-nation board of the International Atomic Energy Agency. The lead U.S. envoy, Geoffrey Pyatt, excoriated the North for abandoning the six-party negotiations.
"We will not accept North Korea as a nuclear weapons state," Pyatt said, according to a statement. "We believe it is in North Korea's own best interests to return to serious negotiations."
Diplomats inside the closed meeting of the IAEA said three of the North's interlocutors -- China, Japan, Russia -- also criticized Pyongyang's nuclear defiance and urged it to return to talks, along with the European Union and Canada.
North Korea, which conducted its first nuclear test in 2006, is believed to have enough weaponized plutonium for at least half a dozen atomic bombs. It disclosed last week that it also is producing enriched uranium, the other pathway to the production of fissile material for nuclear warheads.
Associated Press writers Shino Yuasa in Tokyo, Kelly Olsen in Seoul, George Jahn in Vienna and Steve Gutterman in Moscow contributed to this report.