(Adds further details on trial, sales forecast)

March 26 (Reuters) - Denmark's Novo Nordisk said on Thursday it had decided to submit interim analysis data from a clinical trial of its crucial new insulin drug Tresiba to U.S. regulators within the next month.

The decision is likely to be a relief to investors, since a decision not to file on Tresiba and the related drug Ryzodeg would have further delayed a launch in the world's biggest market.

The U.S. Food and Drugs Administration (FDA) asked Novo to conduct the dedicated cardiovascular risk trial, known as DEVOTE, after refusing to approve Tresiba in 2013 because of worries it might be linked to higher rates of heart attacks or strokes.

Novo had previously said it would decide during the first half of this year whether to submit interim or full trial results. Waiting for full results would have jeopardised its aim of getting to market in 2016.

Tresiba, an ultra-long-acting form of insulin that is also known as degludec, is seen as a crucial future growth driver for the world's top insulin maker as it battles to maintain market share in the face of stiff competition.

Industry analysts forecast it will generate annual sales of $2.2 billion by 2020, according to consensus estimates compiled by Thomson Reuters Cortellis.

Novo noted that results from an interim trial analysis carried a higher level of uncertainty than final study data. "Accordingly, the relative risk estimate that has been derived from the interim analysis is thus only an indication of the final trial results," it said in a statement.

Following the submission, the FDA is expected to communicate either its acceptance of the filing or issue a so-called incomplete response letter within a month.

(Reporting by Ben Hirschler; Editing by David Evans and David Holmes)