North Korea's National Tourism Administration issued the notice to Chinese tour organizers in the middle of last month, said an executive with the Guotai Travel Agency in Dandong, a Chinese border city.

"All tours have been suspended, apart from business and trade groups and groups made up of ethnic Koreans from China," said the executive, who declined to be named.

An official with the Zhongqing Travel Agency, also in Dandong, confirmed North Korea's decision to suspend tour groups.

An official with the China International Travel Service gave a different reason, saying North Korea had explained the quota for Chinese tourists had been used up for this year.

The secretive communist state has been under international pressure since test-firing seven missiles on July 5.

The United States has stepped up pressure on China, the North's closest ally, to take stronger action following the launches and to urge North Korea to return to six-nation talks on ending its nuclear weapons programme.