Asia-Pacific leaders have expressed "strong concern" over North Korea's nuclear weapons test, calling it a clear threat to regional security.
President Bush is keen to win China's support over North Korea
In a statement read out at the end of the Vietnam summit, the leaders urged Pyongyang to honour commitments not to pursue the development of atomic bombs.
US President George W Bush has been seeking support at the summit for UN sanctions against North Korea.
He is trying to persuade Chinese and Russian leaders to take a tougher line.
Mr Bush met Chinese President Hu Jintao and Russian President Vladimir Putin on Sunday.
Meanwhile, the US and Russia have signed a bilateral trade agreement that opens the way for Russia to join the World Trade Organisation.
It has taken 10 years for the two sides to reach this agreement, and correspondents say the accord is a powerful vote of confidence in Russia's investment climate.
The BBC's Bill Hayton in Hanoi says that while trade was the focus of Saturday's talks at the Asia-Pacific Economic Co-operation (Apec), issues of regional security were on the agenda for Sunday.
They have already dominated discussions on the sidelines, he says.
A joint statement on North Korea was read out behind closed doors on Sunday because of some members' sensitivities about interference in other countries.
"We express our strong concern over the 4-5 July missile launches and 9 October nuclear test conducted [by North Korea], which poses a clear threat to our shared interest of peace and security and our shared goal of achieving a nuclear weapons-free Korean peninsula," it was quoted as saying by the Associated Press news agency.
The US denied that the oral statement was a setback for the White House.
"The statement was very firm in the need for full implementation," National Security Council spokesman David McCormick told the agency.
"What was important was that the members of Apec came together on a common statement."
Washington wants to reach a consensus over how to deal with North Korea so that it can present a united front at the next round of six-nation talks on its nuclear weapons programme, expected to take place next month.
Mr Bush held bilateral meetings with both South Korean President Roh Moo-hyun and Japan's Prime Minister Shinzo Abe on Saturday.
The 21 leaders at the summit also discussed ways to tackle bird flu and the Aids epidemic, as well as ways to make Apec more effective.
They said on Saturday they were ready to end a deadlock in world trade talks.
In a joint statement, the Apec heads of state and government said they were ready to move beyond their current positions.
They said they had committed themselves to cuts in agricultural subsidies, the main issue which stalled the so-called Doha round of World Trade Organization (WTO) talks in July.
Mr Bush began the final day of the summit by attending a church service, with his wife Laura and 400 parishioners.
The act was symbolic, our correspondent says, because last week the US state department dropped Vietnam from its list of countries of concern over religious freedoms.
The end of the summit was marked by a photocall for the 21 leaders and a declaration from Vietnam, the host, setting out the non-binding agreements reached by the leaders on a range of issues.