French Socialist presidential frontrunner Francois Hollande toughened his stance on immigration Friday April 27 in a campaign increasingly fought on themes dear to the far right, AFP reported.

Hollande will face right-wing Nicolas Sarkozy in a May 6 run-off for the presidency, and both are scrambling to recruit voters who backed far-right anti-immigrant candidate Marine Le Pen in the first round.

Sarkozy has gone the furthest to reach out to the former pariah, insisting that her values are not incompatible with France's republican tradition, and vowing to secure Europe's borders and fight multiculturalism.

But first-round winner Hollande, attacked by the right for his plan to give foreign residents the vote in local elections, has come under pressure to clarify his stance on immigration and citizenship ahead of a debate next week.

Le Pen did well in Sunday's first-round among white working class voters who might once have backed the left and in a radio interview on Friday the Socialist candidate made a concession to their concerns.

"In the period of crisis we are going through, limiting economic immigration is necessary and essential," he told RTL radio.

"I also want to fight illegal immigration on the economic front. It is not right that a certain number of employers, in a cynical way, are hiring illegal migrants," he said.

Hollande repeated a pledge to ask parliament to cap the number of migrants allowed into France every year - Sarkozy has vowed to halve the number to around 100,000 - but warned it would never halt the flow.

"I don't think there will ever be zero immigration, there will always be legal immigration. Can we reduce the number? That's a debate," he said.