The plans to beef up charges against Chinese-born engineer Chi Mak, 65, his wife, Rebecca Chiu Lai-wah, 62; and Mak's brother, former television director Mak Tai-wing, 56, came at a pre-trial hearing in Los Angeles.

Assistant US Attorney Greg Staples confirmed to US District Judge Cormac Carney that prosecutors intend to upgrade the charges from the current counts of acting as agents for the Beijing government without being registered to do so, a much lesser charge than espionage.

"That's correct," Staples replied when Cormac asked if the US government intended to seek a new indictment containing "more serious charges" against the trio.

Asked when the new charges could be added, Staples responded: "We're talking a matter of weeks."

The three suspects were arrested in October after Mak Tai-Wing was arrested at Los Angeles airport as he and his wife boarded a flight to Hong Kong with an encrypted computer disc in their baggage, prosecutors allege.

The disc contained highly-sensitive data allegedly taken by Chi Mak from a computer belonging to his employer, Paragon, a US military contractor developing secret stealth technology for US warships.

But prosecutors said they are still poring through 40,000 pages of documents seized in searches that only came to light shortly before an indictment was handed down against the trio in November.

Trial for the trio had been scheduled to begin on May 16, but Carney set a new trial date of November 7.

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