BRUSSELS - European Leaders on Friday sided with Madrid amid spiraling tensions prompted by the Catalan parliament's unilateral declaration of independence.

"For EU nothing changes. Spain remains our only interlocutor," European Council President Donald Tusk tweeted. "I hope the Spanish government favors force of argument, not argument of force."

European Commission President Jean-Claude Juncker on Friday stressed the "constitutional order" in a speech at the Conference of Presidents of the Outermost Regions in French Guiana.

"The European Union is first and foremost a set based on the rule of law, respect for it. It's true in the French Republic ... This is also true in Spain. The constitutional order is what it is, it must be respected," he said.

French President Emmanuel Macron, who attended the conference with Juncker, underscored that Spanish Prime Minister Mariano Rajoy is his only interlocutor in Spain, reiterating France's full support to the Spanish government.

"There is a rule of law in Spain, with constitutional rules. Rajoy wants to enforce them and he has my full support," Macron said.

In a separate statement, French Foreign Minister Jean-Yves Le Drian said France "won't recognize the declaration of independence that the Catalan parliament has adopted."

A spokesperson of British Prime Minister Theresa May said Britain will not recognize the Catalan parliament's declaration of independence.

"It is based on a vote that was declared illegal by the Spanish courts. We continue to want to see the rule of law upheld, the Spanish constitution respected, and Spanish unity preserved," the spokesperson added.