Oskar Garcia / AP The home of civilian defense contractor Benjamin Pierce Bishop in Kapolei, Hawaii, is seen at right on March 18, 2013.

A U.S. defense contractor in Hawaii has been arrested on charges of passing national defense secrets, including classified information about nuclear weapons, to a Chinese woman with whom he was romantically involved, authorities said on Monday.

Benjamin Pierce Bishop, 59, a former U.S. Army officer who works as a civilian employee of a defense contractor at U.S. Pacific Command in Oahu was arrested on Friday and made his first appearance in federal court on Monday, the U.S. Attorney's Office for the District of Hawaii said in a news release.

He is charged with one count of willfully communicating national defense information to a person not entitled to receive it, and one count of unlawfully retaining documents related to national defense. If convicted, he faces a maximum of 20 years in prison.

Chinese Foreign Ministry spokesman Hong Lei, asked about the case at a daily news briefing in Beijing, said he did "not understand the relevant situation", and declined further comment.

China and the United States, the world's two largest economies, have long engaged in spying against each other.

Last year China arrested a Chinese state security official on suspicion of spying for the United States, sources said, a case both countries had kept quiet for several months as they strove to prevent a fresh crisis in relations.

That incident ranked as the most serious Sino-U.S. spying incident to be made public since 1985 when Yu Qiangsheng, an intelligence official, defected to the United States.

Yu told the Americans that a retired CIA analyst had been spying for China. The analyst killed himself in 1986 in a U.S. prison cell, days before he was due to be sentenced to a lengthy jail term.

'Person 1'

Bishop met the woman - a 27-year-old Chinese national identified as "Person 1" - in Hawaii during a conference on international military defense issues, according to the affidavit.

He had allegedly been involved in a romantic relationship since June 2011 with the woman, who was living in the United States on a visa, and had no security clearance.

From May of that year through December 2012, he allegedly passed national defense secrets to her on multiple occasions, including classified information about nuclear weapons and the planned deployment of U.S. strategic nuclear systems.

Other secrets included information on the United States' ability to detect foreign governments' low- and medium-range ballistic missiles, as well as information on the deployment of U.S. early warning radar systems in the Pacific Rim.

Bishop had top secret security clearance since July 2002. A court-authorized search of his home in November found around a dozen individual documents each with classification markings at the secret level, the affidavit said.

The case is being investigated by the FBI's Honolulu Division and the Naval Criminal Investigative Service in coordination with U.S. Pacific Command and the U.S. Army.