The US and China must work together on an "effective response" to the sinking of a South Korean warship, US Secretary of State Hillary Clinton has said.
Speaking in Beijing, Mrs Clinton said ensuring peace on the Korean peninsula was "a shared responsibility".
South Korea blames Pyongyang for sinking the Cheonan in March - Pyongyang has denied the charge.
It accused Seoul of trespassing in its waters and said it would respond militarily if "intrusions" continued.
Beijing has repeated its call for all sides to show restraint.
The Cheonan sank near the inter-Korean maritime border on 26 March, with the loss of 46 sailors.
An international panel says a torpedo fired from a North Korean submarine sent the ship down - but Pyongyang has angrily rejected this.
Speaking to reporters in Beijing after two days of wide-ranging talks, Mrs Clinton said the US would "work with the international community and our Chinese colleagues to fashion an effective and appropriate response" to the sinking of the Cheonan.
"The United States and China share the objective of peace and stability on the Korean peninsula," she said.
"Now we must work together again to address the serious challenge provoked by the sinking of the South Korean ship."
China also called for international co-operation over the incident, with Vice Foreign Minister Cui Tiankai saying Beijing was "ready to work together with the US and other parties and continue to stay in close touch on the situation on the Korean peninsula".
State Councillor Dai Bingguo said relevant parties "should proceed on the basis of safeguarding the overall interest of peace and stability in the region, and calmly and appropriately handle the issue and avoid escalation of the situation".
South Korea says it plans to refer North Korea to the UN Security Council, and is seeking a unified international response to the incident.
The US, which has thousands of troops based in South Korea, has backed Seoul, condemning the incident and confirming late on Monday that it will hold joint anti-submarine naval exercises with the country.
But China's attitude is seen as key, because it holds a veto in the Security Council and has in the past been reluctant to impose tough measures on Pyongyang.
South Korea has already suspended trade ties with Pyongyang over the sinking.
It has also resumed propaganda broadcasts to the North, playing radio programmes that will soon to be broadcast via border loudspeakers.
South Korea's defence ministry said the first radio programme, entitled Voice of Freedom, went out on Monday evening. Broadcasts would take place three times a day, a spokesman said.
He said the programme would be broadcast through high-performance loudspeakers that will be installed along the demilitarised zone.
"Initially we are installing loudspeakers at 14 places along the DMZ (Demilitarised Zone). The installation requires several months of work," the spokesman told AFP news agency.
South Korea says it will also drop propaganda leaflets into the North to tell people about the Cheonan incident as soon as possible, and set up giant electronic billboards to flash messages.
Pyongyang has meanwhile accused South Korea of trespassing in its waters.
It said Seoul had sent "dozens of warships" into its waters since 14 May in "a deliberate provocation aimed to spark off another military conflict in the West Sea of Korea and thus push to a war phase the present North-South relations", KCNA news agency reported.
"Should the South side's intrusions into the territorial waters of our side continue, the [North] will put into force practical military measures to defend its waters," it said.
On Tuesday Wu Dawei, China's special representative for Korean affairs, arrived in Seoul for talks with Foreign Minister Yu Myung-hwan.
Mrs Clinton is also due in Seoul for talks on Wednesday, amid considerable tension over the state of inter-Korean ties.