A French state prosecutor has recommended ex-president Nicolas Sarkozy stand trial over alleged irregularities in the funding of his failed 2012 re-election campaign, a judicial source said on Monday.

The recommendation casts a pall over Sarkozy's bid to become president again in a contest scheduled for next April.

The last word on whether Sarkozy stands trial comes down to the investigating magistrate who put the conservative political leader formally under investigation in February.

Now that the Paris state prosecutor's recommendation is finalised, the investigating magistrate, who is independent under France's legal system, is expected to decide in about a month.

That decision would come just weeks ahead of a contest in which Sarkozy, in power from 2007 to 2012, will seek backing as the candidate of his centre-right party, Les Republicains (LR) and its allies.

Sarkozy, 61, formally announced two weeks ago that he was running again for power. He has been accused of breaching spending limits in 2012.

The scandal has become known in France as the Bygmalion affair after the name of a campaign funding company. The affair concerns Sarkozy and 13 other people.

Neither Sarkozy nor lawyers for the ex-president replied immediately to Reuters requests for comment.