North Korea detained a BBC journalist and ordered his expulsion over his reporting, the broadcaster said on Monday, as a large group of foreign reporters cover a rare congress of the country's ruling Workers' Party.Rupert Wingfield-Hayes was detained on Friday as he was about to leave the country, along with a BBC producer and cameraman, the network said. The three were on their way to the airport in Pyongyang on Monday afternoon, it said.

China's Xinhua news agency cited a North Korean official as saying the correspondent was detained for improper "reportage".

Another BBC correspondent in Pyongyang, John Sudworth, said in a broadcast report that there was "disagreement, a concern over the content of Rupert's reporting", including questioning the authenticity of a hospital.

"When he reached the airport on Friday, he was separated from the rest of his team, prevented from boarding that flight, taken to a hotel and interrogated by the security bureau here in Pyongyang before being made to sign a statement and then released, eventually allowed to rejoin us here in this hotel," Sudworth said in the report.

North Korea granted visas to 128 journalists from 12 countries. Their movements are closely managed and as of Monday morning they had yet to get access to the proceedings of the party congress, which began on Friday.

Wingfield-Hayes had been in town ahead of the congress to cover the visit of a group of Nobel laureates.

North Korea said it will strengthen self-defensive nuclear weapons capability in a decision adopted at the congress, its KCNA news agency reported on Monday, in defiance of U.N. resolutions.