An 85-year-old former US army engineer has admitted passing classified military documents to Israel during the 1980s, prosecutors say.

Ben-Ami Kadish was accused of providing the documents, including some relating to US nuclear weapons systems, to an Israeli agent, Yosef Yagur, who photographed them at Kadish's home.

Kadish, who pleaded guilty to only one of the four espionage-related charges he originally faced, entered the plea at a New York court on Tuesday.

He is set to be sentenced in February and could face a maximum of five years in prison and a fine of up to $250,000.

However, a US prosecutor said on Tuesday that the government would not oppose a sentence that means Kadish will not serve time in prison, the Associated Press reported.

Yagur has been linked in court documents to the case of Jonathan Pollard, a US citizen who is serving a life sentence for a 1985 charge of spying for Israel.

Court papers say Kadish's alleged spying took place between 1979 and 1985, although he maintained contact with an Israeli consular official until this year.

Israel has denied spying on the US after 1985.

Classified documents

The charges alleged that the Israeli consular official, identified in the indictment as "CC-1", gave Kadish lists of classified documents to obtain from the US Army's Armament Research, Development, and Engineering Centre at the Picatinny Arsenal in the state of New Jersey.

The documents included information about nuclear weapons, fighter jets and the US Patriot missile air defence system, prosecutors say.

Kadish, who worked at the arsenal from 1963-1990, kept in touch with CC-1 via telephone and email and met the official in Israel in 2004, authorities said.

"CC-1" had left the US in 1985 and has never returned, the US authorities said.