"The best response to the interviews given by the US president is the unity of Europeans, to come together as a bloc," Ayrault said as he went into a meeting of European Union foreign ministers.
Europe should face Donald Trump with "confidence", German Vice Chancellor Sigmar Gabriel said Monday, after the US president-elect had predicted that more EU members would leave the bloc and charged that NATO was "obsolete".
"I think we Europeans shouldn't somehow plunge into a deep, great depression," Gabriel told Bild daily ahead of Trump's inauguration Friday.
"I don't underestimate what Trump says, especially regarding NATO and the EU, but a little bit of self-confidence would serve us well in such a situation."
Ayrault was responding to a hard-hitting interview with two major European newspapers, Trump unleashed a volley of verbal attacks on Europe, dubbing German Chancellor Angela Merkel's refugee policy "catastrophic" and hailing Britain's decision to leave the EU.
But the EU's foreign policy supremo led the European response, insisting the bloc would stand by the nuclear accord, described by Trump as "one of the dumbest deals I have ever seen".
Speaking ahead of a meeting of EU foreign ministers in Brussels, Federica Mogherini said the deal was "proof that diplomacy works and delivers".
"The European Union will continue to work for the respect and implementation of this extremely important deal, most of all for our security," she said.
Trump and Britain
In other remarks, Trump said Brexit "is going to end up as a great thing" and said he backed a trade deal with post-EU Britain, which would be "good for both sides".
"We're gonna work very hard to get it done quickly and done properly," said Trump, confirming he will meet British Prime Minister Theresa May soon after his inauguration.
The pound took a hit Monday in early Asian trade after Britain said it might undercut the EU economically if it cannot obtain both single market access and immigration controls, with British media warning of a so-called "hard Brexit".
"Other countries will leave" the European Union in future, Trump predicted, largely due to the pressure the bloc was put under following a surge in arrivals of migrants and refugees fleeing war, persecution and poverty.
Trump also criticised Merkel for letting Germany admit undocumented migrants into the country, insinuating that this posed a security risk.
"I think she made one very catastrophic mistake and that was taking all of these illegals, you know taking all of the people from wherever they come from. And nobody even knows where they come from," Trump said, adding he had "great respect" for the chancellor.
Critics attacked Merkel after her open-door policy aimed at desperate Syrian refugees brought 890,000 asylum seekers to Europe's biggest economy in 2015, contributing to the rise of an anti-migrant movement.