Carson Block, the short-seller who founded research firm Muddy Waters, on Friday challenged his latest target, Chinese mobile security software company NQ Mobile, to sue him in the U.S.
NQ Mobile's U.S.-listed shares have fallen just over 50 percent since Muddy Waters accused the Chinese firm of fraud last month. The shares closed Thursday at $10.97.
"NQ has sued me in China, which I think a lot of us can admit is basically a joke for them to do that. If they want to hold me responsible, if they feel there is something not right, come and sue me in the U.S.," Block told CNBC Asia's "Squawk Box."
A representative of NQ told CNBC he was unable to comment on any current or potential legal activity.
"Muddy Waters has no known address or phone number; its principal, Carson Block, refuses to disclose where he lives," mobile-security software provider NQ Mobile said in an emailed statement to CNBC prior to the Block interview.
Muddy Waters is a high-profile short-seller, with a long history of targeting companies, mostly Chinese firms listed in the U.S. or Canada, which it claims are fraudulent. In 2011 it released a damaging report accusing Sino-Forest, a Chinese company then listed in Canada, of committing fraud. Sino-Forest's shares fell sharply as a result and the company filed for bankruptcy last year.