Former French prime minister Manuel Valls reacts after partial results in the second round of the French left's presidential primary election in Paris, France, January 29, 2017. REUTERS/Philippe Wojazer

PARIS (Reuters) - Former French Prime Minister Manuel Valls will ask voters to back centrist candidate Emmanuel Macron in the first round of the April-May presidential election, Le Parisien newspaper reported on Monday, citing sources close to Valls.

Valls’ throwing his support behind Macron is a potential blow to ruling Socialist Party candidate Benoit Hamon, who defeated Valls in the party’s January nominating primary.

“Manuel Valls will soon call on voters to support his former rival Emmanuel Macron, and this, from as early as the first round of the election,” Le Parisien said, citing a source in Valls’ primary campaign.

Neither Valls nor Macron’s campaign could be reached for comment. A source close to Valls told Reuters the Parisien report went too far because it was too early and Valls had not decided yet.

Socialist Party official Carlos Da Silva, who was Valls’ substitute in the National Assembly while he was prime minister, said on his Twitter account the Parisien story was false. He did not provide further details.

Both Hamon and Macron were ministers in governments headed by Valls.

Recent opinion polls show Macron as the front-runner in the election and that he will go on to defeat far-right leader Marine Le Pen in a runoff, while Hamon will be eliminated in the first round.