"If we are to make real progress on sending a consolidated message to Iran, we are going to need the support of China," US Assistant Secretary of State Kurt Campbell said on a visit to Beijing.
"We're going to need to see more cooperation and coordination between the United States and China if we are going to be effective in Iran."
China is a close ally of Iran, and has repeatedly opposed sanctions against Tehran over its nuclear programme.
Tehran says the programme is for peaceful nuclear energy, but the West fears it masks a drive to make a nuclear bomb.
Negotiations over the issue have been strained but Iran has recently tried to make a show of greater cooperation since taking part in talks in Geneva with major world powers at the beginning of the month.
Iran and six other nations — Britain, France, Russia, China, Germany and the United States — are to meet at the end of October for a second round of talks aimed at allaying Western concerns over Tehran's nuclear programme.
Campbell was in Beijing for meetings with officials at China's foreign ministry on a range of geopolitical issues and to lay the groundwork for a visit by President Barack Obama next month.
