July 26 (Reuters) - U.S. authorities filed criminal and

civil charges against prominent activist short seller Andrew

Left for an alleged long-running market manipulation scheme

involving bets on stocks including Nvidia ( NVDA ) and Tesla

, they said on Friday.

Left used his Citron Research website and social media

platforms to recommend long or short positions in 23 companies,

telling followers they were consistent with his own positions,

authorities have alleged. Then he and Citron Capital, his

trading firm, quickly reversed positions to capitalize on stock

price movements, they said.

Left for more than a decade has been one of the

prominent so-called "short activists", who say they bet against

public companies on the basis they were overvalued or engaging

in fraud.

Among Left's most high-profile targets were the now

bankrupt China's Evergrande, GameStop ( GME ), Valeant

Pharmaceuticals and Shopify. Fans of short activists say they

play a crucial role in the market, but critics have accused them

of "short and distort" tactics.

Criminal prosecutors have now charged the prominent

activist short seller with multiple counts of securities fraud

for what the DOJ deemed a $16 million market manipulation

scheme, and the SEC separately sued him over a $20 million fraud

scheme, the authorities said in statements on Friday.

Left, 54, declined to comment.

For years, criminal prosecutors in Washington and Los

Angeles and investigators for the SEC have been probing short

sellers over potential market manipulation.

"To maintain the false pretense that Citron's

recommendations and positions were sincerely held, defendant

Left made false and misleading representations and half-truths

about his economic incentives, conviction in Citron's analyses,

and valuations of Targeted Securities," the DOJ said.

Left is expected to be arraigned in the coming weeks in

United States District Court in downtown Los Angeles.

If convicted, he would face a statutory maximum sentence

of 25 years in federal prison for the securities fraud scheme

count, up to 20 years in federal prison for each count of

securities fraud, and up to five years in federal prison for the

false statements count, the DOJ said.