The US Government is investigating reports today that two American journalists have been arrested after crossing the Chinese border into North Korea, a potential diplomatic complication at a time of already high tension over the isolated communist state’s plans to launch a long-range rocket.

A South Korean missionary with contacts in the Chinese border area said that the journalists were Laura Ling and Euna Kim, employees of the California-based cable channel Current TV, who had travelled to China a few days before. The women were apparently arrested by North Korean border guards on Tuesday morning after filming on the Tumen River, which marks the long northeast frontier between the two countries.

Chun Ki Won, a South Korean pastor, said that he had heard that the two women had been arrested along with a local guide. After meeting them in Seoul, he put them in touch with North Korean refugees in China, many of whom had fled across the border over the past decade.

Ms Ling and Ms Kim travelled to the Chinese city of Yanji and apparently went from there to the border. “I told them very clearly not to go to the border because it's dangerous,” Rev Chun told the Associated Press from Washington.

On Thursday last week Ms Ling updated her page on the social networking site Twitter: “Heading to the China/NKorea border,” she wrote. “Hoping my kimchee breath will ward off all danger.”

The US Government expressed its concern at the reports and Swedish diplomats in the North Korean capital, Pyongyang, where the US has no diplomatic representation of its own, were making inquiries on its behalf. “We are working with Chinese government officials in that particular area to ascertain the whereabouts and welfare of the Americans in question,” Fred Lash, a State Department spokesman said. “We've also been in touch with North Korean officials to express our concern about the situation.”

The impact of the incident will depend on the circumstances of the two women’s arrest. If, as South Korean television reported, North Korean guards crossed the border to seize the two women, it will anger the Chinese Government at a time of diplomatic engagement with Pyongyang. The North Korean Prime Minister, Kim Yong Il (not to be confused with the supreme leader, Kim Jong Il), is in Beijing for talks this week and met yesterday with Hu Jintao, the Chinese President.

If the women crossed the border themselves, it is the US that will be embarrassed at a moment when it is demanding that North Korea abandon its plans to fire a long-range rocket across the Pacific. In 1996 an American missionary named Carl Hunziker was arrested after swimming across the river in a drunken prank. He was held for three months and released when the present Governor of New Mexico, Bill Richardson, travelled to Pyongyang and negotiated with the North Koreans.

In 2001, by contrast, an Italian photographer was released within four days - after responding to beckoning soldiers and crossing the river, only to be promptly arrested.

Despite its intense xenophobia and isolation, North Korea’s border with China is remarkably porous. During the summer the Tumen and Yalu rivers that mark it are reduced to a few yards of water and in the winter they freeze, allowing goods and people to pass illegally in both directions. Many of them are North Korean defectors fleeing oppression or seeking asylum elsewhere.

In 2000 Kim Dong Shik, an American pastor who helped refugees to escape, was reported to have been abducted by North Korean agents and taken back with them to an unknown fate.

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