Former US ambassador to the UN Bill Richardson urged the United States on Saturday to engage in dialogue with North Korea, but only if Pyongyang refrains from further nuclear tests and missile launches.

Richardson, a former New Mexico governor, and Google chairman Eric Schmidt visited North Korea last month in an unsuccessful bid to free Kenneth Bae, an American of Korean descent, who is being held in North Korea.

Upon his return, Richardson has concluded that the lack of direct dialogue between the US and North Korea is not helping Washington achieve its goals.

"Dialogue is not an endorsement or legitimization of your counterpart's positions," the ex-UN envoy wrote in The Washington Post. "Rather, it is an exchange of arguments and ideas that help both sides better understand the other and identify opportunities."

However, in Richardson's view, this dialogue should not be unconditional.

"First and foremost, the North Koreans should refrain from performing any additional nuclear tests or ballistic missile launches," he stressed. "If North Korea's leader truly intends to refocus on economic development for his people, he needs to break the cycle of escalation."

Richardson believes the United States cannot rely on China to prevent nuclear proliferation. In his view, issues such as zones of influence and refugees complicate the Chinese-North Korean relationship.

According to Richardson, recent public statements in both South and North Korea hint at a renewed interest in dialogue.

While he approved of recently strengthened UN sanctions against Pyongyang in response to its ballistic missile launch, the former diplomat also argued for keeping all diplomatic options open.

"While sanctions are merited and are a legitimate tool, so is dialogue," he said. "The two are not mutually exclusive."

Richardson noted that much of what he saw recently in Pyongyang was staged, but not everything.

While members of the foreign ministry constantly escorted the US visitors, he recalled, they still got a couple of chances to interact with citizens during their daily activities.

He said the Americans had taken a semi-spontaneous ride in the subway system, saw acclaimed acrobats perform an adaptation of a feudal love story in front of thousands of families in a freezing theater, and viewed children playing in the snow in the streets.

"Our societies are very different, no doubt," he wrote in conclusion. "But North Koreans desire and deserve a better quality of life than the one they have. And if their young leader is true to the statements he has made to his people about improving their livelihood, the first thing he should do is break the cycle of escalation, refrain from additional tests and, along with the United States, engage in direct dialogue."

Richardson has visited North Korea several times in the past two decades and has been involved in negotiating the release of US citizens held in the isolated country.

Before his January visit, he went to North Korea in 2010 when he met its chief nuclear negotiator to try and ease tensions after the country shelled a South Korean border island.

The appeal comes as a new foreign policy and national security team is beginning to take shape in Washington as President Barack Obama begins his second term in office.

Former Democratic Senator John Kerry was sworn in Friday as America's new secretary of state, less than two hours after Hillary Clinton left that office.

Another former senator, Chuck Hagel, has been tapped by Obama to lead the Pentagon.

At the same time, John Brennan, the president's counter-terrorism adviser, was nominated as the Central Intelligence Agency's next director to replace David Petraeus, who had resigned over an extramarital affair.