Reaction by European leaders to Sunday's independence referendum in Catalonia was mixed, with some strongly condemning the use of force by Spanish police to halt the vote and others commenting warily, mindful of separatist movements in their own countries or the EU.

About midday on Monday, roughly 24 hours after clashes broke out, the EU's executive European Commission released a statement saying the vote in Catalonia was not legal under Spain's constitution and that the Commission considered it an internal matter for Spain.

Click here to view the referendum as it happened

"We call on all relevant players to now move very swiftly from confrontation to dialogue. Violence can never be an instrument in politics. We trust the leadership of Prime Minister Mariano Rajoy to manage this difficult process in full respect of the Spanish Constitution and of the fundamental rights of citizens enshrined therein," the Commission statement said.

"Beyond purely legal aspects, the Commission believes that these are times for unity and stability, not divisiveness and fragmentation."

European Council President Donald Tusk later announced on Twitter that he had spoken with Rajoy, calling for a bid to find ways "to avoid further escalation and use of force." 

Read more: Catalan independence - what you need to know

Germany's position

German Foreign Minister Sigmar Gabriel on Monday released a statement echoing the EU's calls for dialogue. 

"The images that reached us yesterday from Spain show how important it is to interrupt the spiral of escalation," Gabriel said.

Opinion: Spain versus Catalonia – An epidemic of insanity

On Monday, Greens co-leader Cem Özdemir, a potential coalition partner for Chancellor Angela Merkel and future senior minister, outright condemned the force used.

"Whether or not the referendum was legitimate, the violence by police against voters was disproportionate and harmful to such an important dialogue," he wrote on Twitter.

Marked differences in UK reactions

UK Foreign Secretary Boris Johnson said it was a matter for the Spanish government and people and that it was important the Spanish constitution be respected and the rule of law upheld. Madrid had ruled Catalonia's referendum illegal.  

Scotland's First Minister Nicola Sturgeon criticized the statement as "shamefully weak." Sturgeon closely followed Sunday's events on her Twitter feed, saying she was increasingly concerned by the images coming from Catalonia.

"Regardless of views on independence, we should all condemn the scenes being witnessed," Sturgeon, who led Scotland's 2014 independence referendum in which it voted to remain part of the UK, said.

Guy Verhofstadt, an EU lawmaker who is leading the European Parliament's Brexit negotiations, called for de-escalation and a negotiated solution to the conflict.

"In the European Union we try to find solutions through political dialogue and with respect for the constutional order," he said.

Support and concern directed at Madrid

Outside the EU, Serbia's foreign minister has expressed support for Madrid.

"Our position is clear and principled, Spain is one of the greatest friends of Serbia," Ivica Dacic said, adding that Madrid is in "the same position on the issue of the territorial integrity of Serbia."

Spain, unlike most other EU member states, does not recognize the independence of Kosovo, which broke away from Serbia in 2008.

The United Nations human rights chief, Zeid Ra'ad Al Hussein urged Madrid to investigate Sunday's violence, saying he was "very disturbed" by it.

"I urge the Spanish authorities to ensure thorough, independent and impartial investigations into all acts of violence," he said. "Police responses must at all times be proportionate and necessary."

Local authorities in Catalonia reported that hundreds of citizens had been injured as police attempted to halt voting in the referendum, which had been outlawed by Spain's Constitutional Court. Catalan's government pressed ahead with the vote despite firm opposition from the central government in Madrid. Amid a low voter turnout of 42.3 percent, some 90 percent voted for independence. Catalonia's leader Carles Puigdemont said the result paved the way to independence from Spain.

se/rt (dpa, AFP, Reuters, AP)