NEW YORK, April 4 (Reuters) - Swiss drugmaker Novartis AG sued Amgen Inc on Thursday, accusing the U.S. biotech of trying to back out of the companies' agreements to develop and market Aimovig for the prevention of migraines.

In a complaint filed in Manhattan federal court, Novartis accused Amgen of improperly trying to terminate their collaborative agreements, which began in 2015, in an effort to keep Aimovig profits for itself. Aimovig won U.S. approval last year.

(Reporting by Jonathan Stempel in New York; editing by Bill Berkrot)