NEW YORK, Feb 10 (Reuters) - A Manhattan federal jury on Monday ruled in favor of Denmark's tax authority, in the first U.S. civil trial concerning the country's effort to recoup about $2.1 billion of tax refunds it claims were obtained through fraud, court records show.

Jurors sided with SKAT, the Danish equivalent of the U.S. Internal Revenue Service. Further information was not immediately available.

The trial arose from complex arbitrage transactions known as "cum-ex" trades whose accused mastermind, British hedge fund trader Sanjay Shah, was sentenced by a Danish court in December to 12 years in prison after being found guilty of fraud.

SKAT said pension plans used the trading strategy between 2012 and 2015 to make it falsely appear they bought tens of billions of dollars of Danish companies' stock, and then claimed refunds on taxes supposedly paid on dividends.

Lawyers for SKAT and for the pension plan defendants did not immediately respond to requests for comment.

Jurors reached their verdict on the second day of deliberations. The trial began on January 7.

(Reporting by Jonathan Stempel in New YorkEditing by Matthew Lewis)

((jon.stempel@thomsonreuters.com; +1 646 223 6317; Reuters Messaging: jon.stempel.thomsonreuters.com@reuters.net))