US President Barack Obama has urged North Korea to give up developing nuclear weapons if it wants better relations with United States.

美国总统奥巴马呼吁如果朝鲜想与美国改善关系，那就停止核武器的研究。

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Barack Obama praised Mr Clinton's "extraordinary humanitarian effort"

Mr Obama said North Korea should not engage "in provocative（挑拨的，刺激的） behaviour".

He was speaking hours after former US President Bill Clinton had secured the release of two US journalists during his surprise visit to Pyongyang.

The reporters, who were convicted of illegally entering North Korea, are now reunited with their families in the US.

"We have said to the North Koreans there's a path for improved relations and it involves them no longer developing nuclear weapons," Mr Obama told US TV network MSNBC.

"We just want to make sure the government of North Korea is operating within the basic rules of the international community," he added.

Diplomatic game

The BBC's Daniel Sandford in Washington says that it appears that the two US reporters were used fairly cynically³（爱嘲笑地，冷笑地） by Pyongyang as pawns⁴（典当，人质） in a diplomatic game.

Pyongyang dropped out of six-party talks after the UN censured⁵（责难，非难） a long-range missile test in April. The talks include Russia, China, Japan, the US and both Koreas.

An underground nuclear test and further missile tests followed, provoking（激怒人的，刺激人的） new UN Security Council sanctions（制裁）.

Mr Obama was speaking shortly after the two reporters - 36-year-old Euna Lee and Laura Ling, 32, - touched down at Los Angeles airport. They had travelled from Pyongyang on a chartered plane（包机） alongside Mr Clinton.

The journalists - who were sentenced in June to 12 years hard labour - were able to leave Pyongyang after North Korean leader Kim Jong-il granted them a special pardon.

In Los Angeles, tears flowed as they walked down the steps and into the arms of their families.

'Nightmare'

Ms Ling spoke⁶ on behalf of both journalists, describing their surprise and relief at being taken to a meeting in North Korea to find Mr Clinton standing⁷ in the room.

"We were shocked. But we knew instantly in our hearts that the nightmare of our lives was finally coming to an end," she said.

Thanking Mr Clinton and his staff, Ms Ling said the pair would now spend some "private, quiet" time with their families.

"The past 140 days have been the most difficult and heart-wrenching（令人心碎的，令人心痛的） times of our lives," she said.

The two reporters were arrested by North Korean guards while filming a video about North Korean refugees for Current TV.

In Pyongyang, the official North Korean News Agency (KCNA) said their release was a sign of the country's "humanitarian and peace-loving policy".

Mr Clinton's unannounced visit to Pyongyang had been described as a private mission but a White House official later confirmed that North Korea had asked Mr Clinton to visit.

A senior US official said President Obama had been aware of the mission from its early stages and that US allies involved in the six-party talks over North Korea's nuclear programme were also informed.

US officials earlier said the North Korean government had agreed in advance that Mr Clinton's mission would not touch on the question of its nuclear programme.

Speaking as she arrived in Kenya at the start of a tour of Africa, US Secretary of State Hillary Clinton welcomed the release and said that she had briefly⁸ spoken to her husband.