SEOUL (Reuters) - A U.S. citizen who said he illegally entered North Korea held a press conference in Pyongyang on Sunday to deliver a 4,000-word statement denouncing U.S. domestic and foreign policy, CNN said.

CNN said the man identified himself as Arturo Pierre Martinez, 29, from the U.S. border town of El Paso. His mother told CNN her son was bipolar, and had previously tried to enter North Korea from the South Korean side.

"He is very smart and he got the court to let him out and instead of coming home to us he bought a ticket and left for China," the television news channel quoted Patricia Eugenia Martinez as saying.

No official statement had been released by North Korean media as of early Sunday afternoon.

In September, South Korean media reported that a man in his late 20s had been arrested by South Korean marines for swimming in a river that flows towards North Korea. The man had been trying to go to the North to meet its leader, local media reported at the time.

It was not immediately clear how or why Martinez entered North Korea. A North Korean statement seen by CNN said Martinez entered the country two days after U.S. intelligence official James Clapper arrived in Pyongyang to negotiate the release of detained Americans Matthew Miller and Kenneth Bae.

Miller and Bae had both been serving hard labor sentences in North Korea for breaking local laws, but were released in November. A third detained U.S. citizen, Jeffrey Fowle, was released in October.

"(I am) extremely grateful for having been pardoned from the punishments given to violators of these laws, and for the most generous reception I have received," CNN reported Martinez as saying in his statement, which criticized America's politicians, police, foreign policy and the electoral system.

(Reporting by James Pearson; Editing by Simon Cameron-Moore)