The US National Security Agency has spied on French diplomats in Washington and at the UN, according to the latest claims by French daily Le Monde, reports BBC News.
NSA internal memos obtained by Le Monde detailed the use of a sophisticated surveillance programme, known as Genie.
US spies allegedly hacked foreign networks, introducing the spyware into the software, routers and firewalls of millions of machines.
It comes a day after claims the NSA tapped millions of phones in France.
The details in the latest Le Monde article are based on leaks from ex-intelligence analyst Edward Snowden, through Glen Greenwald, the outgoing Guardian journalist, who is feeding the material from Brazil, says the BBC's Christian Fraser in Paris.
It comes on the day the US Secretary of State, John Kerry, is in London meeting foreign counterparts to discuss Syria.
The Le Monde report sets out details of Genie, an NSA surveillance programme in which spyware implants were introduced remotely to overseas computers, including foreign embassies.
t claims bugs were introduced to the French Embassy in Washington (under a code name "Wabash") and to the computers of the French delegation at the UN, codenamed "Blackfoot".
The article suggests that in 2011, the US allocated $652m (£402m) in funding for the programme, which was spent on "spy implants". Tens of millions of computers were reported to have been hacked that year.
A document dated August 2010 suggests intelligence stolen from foreign embassy computers ensured the US knew ahead of time the positions of other Security Council members, before a UN vote for a resolution imposing new sanctions on Iran.
The US was worried the French were drifting to the Brazilian side - who were opposed to implementing sanctions - when in truth they were always aligned to the US position, says our correspondent.
The intelligence agency quotes Susan Rice, then-US ambassador to the UN, who praises the work done by the NSA: "It helped me know... the truth, and reveal other [countries'] positions on sanctions, allowing us to keep one step ahead in the negotiations."
On Monday, Le Monde alleged that the NSA spied on 70.3 million phone calls in France between 10 December 2012 and 8 January 2013.
At a breakfast meeting with the US secretary of state on Tuesday, French Foreign Minister Laurent Fabius demanded a full explanation.
Referring to a telephone call between the French and US presidents, Mr Fabius told reporters: "I said again to John Kerry what Francois Hollande told Barack Obama, that this kind of spying conducted on a large scale by the Americans on its allies is something that is unacceptable."
Asked if France was considering reprisals against the US, government spokeswoman Najat Vallaud-Belkacem replied: "It is up to Foreign Minister Fabius to decide what line we take but I don't think there is any need for an escalation.
"We have to have a respectful relationship between partners, between allies. Our confidence in that has been hit but it is after all a very close, individual relationship that we have."
Both French officials made their comments before the latest revelations appeared in Le Monde.
Read more of this report from BBC News.