Lisbon (AFP) - French President Francois Hollande urged Europe to form a united front and provide a "firm" response to US President Donald Trump, at a gathering Saturday of southern European Union leaders.

"We must conduct firm dialogue with the new American administration which has shown it has its own approach to the problems we all face," he said at the end of the gathering as he was flanked by the other leaders who took part.

Trump has rattled America's traditional European allies with a range of radical policy plans.

He has called NATO "obsolete", announced he would rip up a planned transatlantic trade plan and supported Britain's move to leave the EU, praising the decision as "a wonderful thing" during a meeting Friday with British Prime Minister Theresa May.

On Friday he also signed a sweeping executive order to suspend the arrival of refugees and impose tough controls on travellers from seven Muslim countries.

During his first phone conversation with Trump late Saturday, Hollande stressed the "economic and political consequences of a protectionist approach", adding that the principle of "acceptance of refugees" should be respected.

"Faced with an unstable and uncertain world, withdrawal into oneself is a dead-end response," Hollande was quoted as saying in an Elysee Palace statement.

Hollande had earlier told the gathering that "when he adopts protectionist measures, which could destabilise economies not just in Europe but the economies of the main countries of the world, we have to respond".

"And when he refuses the arrival of refugees, while Europe has done its duty, we have to respond."

- Ready to cooperate with Trump -

While officially the new administration in Washington was not on the agenda, the six other European leaders who took part in the summit also alluded to Trump.

Italian Prime Minister Paolo Gentiloni said Europe was "ready, interested and willing to cooperate" with the Trump administration.

"But we are Europe, and we cherish our values," he added.

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Spanish Prime Minister Mariano Rajoy defended the EU project, saying it had helped transform Europe into the world region with the "highest level of progress, civil rights and well being".

Also meeting in Lisbon were the leaders of Malta, Cyprus, Greece and Portugal.

The summit was a follow up to a first gathering in Athens in September 2016 as part of a push by Greek Prime Minister Alexis Tsipras to create a strong southern "axis" to counter the influence of nations in northern Europe.

The group is often referred to -- sometimes dismissively -- as "Club Med", even though one of its members, Portugal, is not on the Mediterranean.

It includes some of the nations hardest hit by the financial crisis.

Portugal and Greece both needed international bailouts worth tens of billions of euros which came with demands for tough austerity measures and economic reforms.

- Boost investment -

As in the first meeting in Greece, the mostly centre-left leaders gathered in Portugal urged Brussels to do more to boost flagging growth in the bloc.

A joint declaration signed by the participating countries said the EU should boost funding for strategic investment.

"We share the urgency of promoting investment, growth, employment, with a special focus on youth employment," it read.

The Lisbon summit comes ahead of a February 3 meeting of EU leaders in Malta to look at the future of the bloc without Britain, its second-largest economy and its richest financial centre.

Rajoy said Madrid would host a third summit of southern EU nations in April.

"These countries meet informally and they have no other goal other than to work for the people of the entire European Union," he said.

The goal is not to create an "organisation" inside Europe but to act "in the service of the entire European Union," added Hollande.

The so-called Visegrad group -- made up of Hungary, Slovakia, the Czech Republic and Poland -- have also held their own meetings to present a united front.