China should use its influence over North Korea to defuse the crisis sparked by the North's shelling of a Southern island, US officials say.
State department spokesman PJ Crowley said Beijing's role was pivotal and urged Beijing to be clear on the issue.
China is the only nation with influence in the North but Beijing has so far issued statements urging restraint and has refused to blame the North.
Two South Korean civilians and two marines died in Tuesday's shelling.
The burnt bodies of two men in their 60s were found on Wednesday on the island, which lies near the disputed Yellow Sea border.
The latest TV pictures of the island show neighbourhoods reduced to rubble with shops and homes burnt and destroyed.
The US, which is due to hold joint military drills with the South from this Sunday, urged China to take a tougher stance with its ally.
"China does have influence with North Korea and we would hope and expect that China will use that influence," said Mr Crowley.
"First to reduce tensions that have arisen as a result of North Korean provocations and then secondly [to] continue to encourage North Korea to take affirmative steps to denuclearise."
Mr Crowley described the shelling as a "one-off, premeditated act" and said the US did not think Pyongyang was preparing for an extended military confrontation.
Japanese officials have also encouraged China to take the lead with Pyongyang.
Earlier, Chinese Foreign Ministry spokesman Hong Lei said they "regret the casualties and property losses, and are concerned about the situation".
"We strongly urge both sides retain calm and restraint and engage in talks as quickly as possible in order to prevent similar incidents from happening again," Mr Hong said in a statement carried by state-run Xinhua news agency.
At least 18 people were injured in Tuesday's attack.
Hundreds have since fled the island, taking ferries to the mainland where they described what happened.
"I heard the sound of artillery and I felt that something was flying over my head," said Lim Jung-eun, a 36-year-old housewife who fled the island with her three children. "Then the mountain caught on fire."