China and Russia have long backed North Korea but may be losing patience
Russia and China have urged North Korea to return to the negotiating table over the future of its nuclear programmes.
In a joint statement the two powers expressed "serious concern" about tensions on the Korean peninsula.
Their move came after North Korea had threatened a "thousand-fold" retaliation against the US and its allies if Pyongyang were provoked.
China and Russia have already signed a United Nations resolution approving tougher sanctions against North Korea.
The reclusive state held a nuclear test and launched missiles in May, has torn up peace agreements signed after the Korean War in 1953, ejected international nuclear energy monitors, and threatened more tests.
China and Russia issued their joint statement after a series of meetings in Russia. Nine out of 14 pages focused on economic issues.
These included a deal for Russia to supply China with oil for 20 years, and cooperation agreements in coal and natural gas production.
Time to talk
The statement issued by Chinese President Hu Jintao and Russian President Dmitry Medvedev pressed for a peaceful resolution of the Korean standoff and the "swiftest renewal" of the now-frozen six-party 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.
Analysts said the direct mention of concern about developments in North Korea was a clear sign of growing impatience with Pyongyang even among its allies.
In Vienna, at a meeting of the International Atomic Energy Agency, diplomats said China and Russia joined other nations in calling on North Korea to return to talks.
The Chinese delegate said the international community needed to respect North Korea's sovereignty, but urged the Pyongyang regime to come back to the table "and the rest of us to show calm and restraint," a diplomat told reporters.
North Korea stopped cooperating with the IAEA in mid-April, ordered the agency to remove all containment and surveillance equipment from the Yongbyon nuclear facilities and asked IAEA inspectors to leave the country.
North-eastern China, and Russia's Far East, share borders with North Korea.
China has long been a rare friend to North Korea, having fought on its side against US-led forces in the Korean War of 1950 to 1953.
Moscow was one of North Korea's strongest backers during the Cold War. After the 1991 Soviet collapse, China was the only country with any real clout with North Korea, although Moscow has tried to nurture ties in recent years.
This week, North Korea threatened a "thousand-fold" military retaliation against the US and its allies if it is provoked.
The warning came after US President Barack Obama said that a nuclear-armed North Korea posed a "grave threat" to the world.