The Taoiseach Leo Varadkar has congratulated Prime Minister Pedro Sánchez on his election victory in Spain.
The ruling Socialists secured the most votes in the country's general election, but failed to win a majority amid historic gains by the far-right.
In one of the country's most hotly contested elections in decades, Mr Sánchez's PSOE party took 123 seats in the 350-seat parliament with nearly 29% of the vote.
The new far-right Vox party made its national breakthrough by capturing about 10% of the vote, winning 24 seats.
It is the first time a far-right party will enter parliament in Spain since the country's transition to democracy following the death of dictator Francisco Franco in 1975.
The conservative Popular Party - once the leading force in Spain's parliament - recorded its worst ever showing in a national vote with 66 seats, losing half of its support since the last election in 2016.
Meanwhile, the centre-right Ciudadanos party took 57 seats and the far-left Unidas Podemos (United We Can) secured 35 seats.
In a tweet, Mr Varadkar said he looked forward to continuing to work together, before remarking that "Mainstream pro-EU parties won. Far right came 5th behind the left, right, centre and radical left. Let's not give them too much attention".
Congratulated @sanchezcastejon on election victory in Spain. Look forward to continuing work together at EU Council and return visit to Dublin.Mainstream pro-EU parties won. Far right came 5th behind the left, right, centre and radical left. Let’s not give them too much attention
— Leo Varadkar (@LeoVaradkar) April 29, 2019
Vox leader Santiago Abascal celebrated his party's results at an election night rally in Madrid, telling supporters he had insisted his party were "going to begin a reconquering of Spain and that's what we have done".
The far-right party formed five years ago and has promised to defend Spain from its "enemies" citing feminists, liberal elites and Muslims among others.
The election result means that Mr Sánchez will be able to enter negotiations for an alliance with the anti-austerity Unidas Podemos, whose leader has offered to share a coalition cabinet.
Vox leader Santiago Abascal casts his ballot at a polling station in Madrid, Spain | Image: Jorge Gonzalez Moreno/Xinhua News Agency/PA ImagesMr Sánchez said the only conditions he would place on forming a coalition government would be respecting the constitution and promoting social justice.
Spain's interior ministry said that turnout was over 75% - well above the average in the previous 12 elections since Spain returned to democratic rule.
It is the country's third general election in four years.
Voters in Spain have become disillusioned as the country struggled with a recession, austerity cuts, corruption scandals, the divisive Catalan independence demands and a rise in far-right Spanish nationalism.
As a result, after having only two main political parties for decades, the Socialists and Popular Party, Spain's political landscape has fragmented into five leading parties.
Mr Sánchez called the election after his national budget was rejected in the lower chamber by the centre-right conservative opposition and Catalan separatists who are fighting for independence.
Polls a week ago showed about one-third of almost 37 million eligible voters had not decided how they would vote.
Speaking after he voted on Sunday, Mr Sánchez said he wanted the election to provide a parliamentary majority that can undertake social and political reforms in the country.
He said he hoped the lower house would support "a stable government that with calmness, serenity and resolution looks to the future and achieves the progress that our country needs in social justice, national harmony and political cleansing".
Main image: Spain's Prime Minister Pedro Sánchez speaks to supporters at the headquarters of the Spanish Socialist Party (PSOE) in Madrid, Spain | Image: Guo Qiuda/Xinhua News Agency/PA Images
