MEPs have been quick to condemn the violence that erupted as a result of Catalonia's independence referendum on 1 October.
Spanish riot police had stormed voting offices and arrested Catalan officials, in a bid to stop the poll, deemed unconstitutional by Spanish courts.
A Catalan spokesperson announced that 43 per cent of those eligible to vote had taken part, out of whom more than 90 per cent voted in favour of independence.
Catalan President Carles Puigdemont vowed to declare independence for the region, amid increasingly violent clashes between Spanish police and civilians. The Spanish government has insisted the referendum is not legally binding and that it would not recognise Catalan independence.
On Monday, thousands of people took to the streets in cities across Europe to protest the Spanish government's handling of the situation.
On Twitter, many were calling for Spanish Prime Minister Mariano Rajoy to step down using the hashtag '#RajoyDimisión'.
The European Commission has declined to comment on the issue, saying it is an internal matter to be dealt with by Spain.
This prompted many angry reactions from MEPs.
S&D group leader Gianni Pittella said, "This is a sad day for Spain and for the whole of Europe. There is no doubt that the non-referendum organised and supported by the Catalan authorities is to be considered illegal and invalid. However, the feelings of so many Catalans that took to the streets must also be heard.
"The solution can only be a political response, not a police one. However for months Spanish Prime Minister Rajoy has done nothing. The escalation of the tension should have been diffused a long time ago, in order to avoid clashes between the police and civilians.
"The awful images of violence broadcast from Barcelona worldwide should never have happened. It is disgraceful that the conservative government in Spain did not open a dialogue before and disregarded the voice of so many citizens in Catalonia. On the other hand, the Catalan Authorities led citizens along an illegal path despite the many judgements issued by not only the Spanish Constitutional Court but also Catalan Tribunals."
ALDE group Chair Guy Verhofstadt - whose group includes Catalan separatist MEPs - commented, "I don't want to interfere in the domestic issues of Spain but I absolutely condemn what happened today in Catalonia. The separatist parties went forward with a so-called referendum that was forbidden by the Constitutional Court, knowing all too well that only a minority would participate as 60 per cent of the Catalans are against separation. [But I also condemn] the use of disproportionate violence to stop this."
Greens/EFA group co-Chairs Ska Keller and Philippe Lamberts said, "This is a political problem and it needs to be solved politically, not by police force. The European Commission can't continue to turn a blind eye on the situation in Catalonia. We urge the Commission to promote dialogue and to offer mediation."
Several MEPs backed proposals to debate the crisis during this week's plenary.