French President Francois Hollande on Friday criticised "unacceptable" pressure on the European Union from his US counterpart Donald Trump, who has predicted a break-up of the bloc.
"It is unacceptable that there should be, through a certain number of statements by the president of the United States, pressure on what Europe should or should not be," Hollande told reporters at an EU summit in Malta.
"Who really knows what the US president wants, particularly for the transatlantic alliance, and on the sharing of expenses that he calls a burden," Hollande added.
German Chancellor Angela Merkel meanwhile said the best way for the 28-nation bloc to deal with a US administration that seems ambivalent to Europe is to push forward with its own plans.
"I already said that Europe has its destiny in its own hands," Merkel told reporters as she arrived in Valletta.
"And I believe the stronger we state clearly how we define our role in the world, the better we can take care with our transatlantic relations," she added.
"That is why for me, talks about Europe are here in the foreground and not to deal with other parts of the world."
In Malta, the EU leaders are to discuss relations with Trump during the second half of the summit, after major talks about cutting illegal migration across the Mediterranean from Libya.
Trump has alarmed many in Europe by previously backing Britain's decision to leave the EU, predicting that more countries will jump ship and calling the US-led NATO military alliance "obsolete".