* Messenger app firm has already filed for Japan IPO
* Sources say dual US-Japan listing or US-only listing likely (Updates with response from Line, Naver. Adds background)
SEOUL, July 18 Line Corp, a Japan-based social messaging service firm, has filed for an initial public offering in the United States, Bloomberg news reported on Friday, citing unidentified sources.
Line's parent company, South Korea's Naver Corp, said on Wednesday that Line had filed for an initial public offering in Tokyo.
Banking sources with direct knowledge of the matter told Reuters on Wednesday that the listing will ultimately be either a dual U.S.-Japan listing or a listing only in the United States.
One of the banking sources told Reuters on Tuesday that Line the IPO would value the company between 1 trillion and 2 trillion yen ($10 billion-$20 billion).
Morgan Stanley is managing the U.S. share sale, Bloomberg said, noting that companies with less than $1 billion in revenue can submit their filings privately under the Jumpstart Our Business Startups Act. It was not clear which U.S. exchange it would list on.
Both Line and Naver declined to comment on the report.
The Line messaging app has been downloaded 480 million times, with growth of 140 percent over the last year, making it one of the world's most popular messaging services, albeit with comparatively low exposure in the United States
Line's app posted 14.6 billion yen ($145 million) in revenue in January-March - a more than threefold increase on the year. The app's full-year sales hit 34.3 billion yen last year, becoming the highest-grossing non-game app of 2013, according to analytics firm App Annie. (Reporting by Se Young Lee in Seoul and Teppei Kasai in Tokyo; Editing by Edwina Gibbs)