Iñigo Urkullu, leader of the Basque Nationalist party, casts his vote in the regional elections. Photograph: Ander Gillenea/AFP/Getty Images

Separatist tensions within the European Union looked set to grow with a surge of support for pro-independence parties at regional elections held on Sunday in Spain‘s northern Basque country.

A separatist coalition, EH Bildu, became the region’s second biggest political group, taking a quarter of the vote as it reaped a peace dividend following armed separatist group Eta‘s decision to end four decades of terrorism last year.

The coalition brings together peaceful separatists with former members of Eta’s political wing who are no longer banned from parliamentary politics. It won 21 of the 75 seats in the regional parliament.

The moderate Basque Nationalist party (PNV), which backs a gradual march towards an as yet undefined form of independence, lost votes to EH Bildu but was the overall winner with a third of the votes and 27 seats.

PNV looked set to form a minority government, possibly supported by EH Bildu, though party leader Iñigo Urkullu has refused to say exactly how he plans to govern. The two parties jointly won almost two-thirds of the seats, bringing an end to three years of socialist government under outgoing Basque prime minister Patxi López.

Although Urkullu has pledged to make the economy his first priority, he was widely expected to follow the example of Catalan regional president Artur Mas and call some kind of referendum on independence over the coming four years.

Read more