US President Barack Obama on Wednesday moved to defuse tensions after revelations of US spying on three French presidents angered France, while WikiLeaks founder Julian Assange called for legal action.

US President Barack Obama on Wednesday moved to defuse tensions after revelations of US spying on three French presidents angered France, while WikiLeaks founder Julian Assange called for legal action over Washington's snooping and promised more disclosures to come.

Obama spoke by phone with his French counterpart Francois Hollande to assure him the US was no longer spying on European leaders, a day after the WikiLeaks website published documents alleging Washington had eavesdropped on the French president and his two predecessors.

"President Obama reiterated without ambiguity his firm commitment... to stop these practices that took place in the past and which were unacceptable between allies," Hollande's office said in a statement.

Hollande had earlier convened his top ministers and intelligence officials to discuss the revelations, with his office stating France "will not tolerate any acts that threaten its security".

France's foreign ministry also summoned the US ambassador for a formal explanation.

The documents - labelled "Top Secret" and appearing to reveal spying on Jacques Chirac, Nicolas Sarkozy and Hollande between 2006 and 2012 - were published by WikiLeaks along with French newspaper Liberation and the Mediapart website.

WikiLeaks' anti-secrecy campaigner Assange told French television late Wednesday the time had come to take legal action against Washington over its foreign surveillance activities.

Assange also said other important revelations were coming.

"This is the beginning of a series and I believe the most important of the material is still to come," he said.

The WikiLeaks revelations were embarrassingly timed for French lawmakers, who late on Wednesday voted in favor of sweeping new powers to spy on citizens.

The new law will allow authorities to spy on the digital and mobile communications of anyone linked to a "terrorist" inquiry without prior authorization from a judge, and forces Internet service providers and phone companies to give up data upon request.

The White House earlier responded that it was not targeting Hollande's communications and will not do so in the future, but it did not comment on past activities.

Leaks by whistleblower Edward Snowden in 2013 about spying on European leaders, revealed by, had already led to promises from Obama that the practice had stopped.