Heads of state from 21 EU countries have urged voters to reverse the downward trend in turnout in European Parliament (EP) elections.

The group, including Czech and Polish eurosceptics, also praised EU values and attacked nationalism.

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Czech president Milos Zeman (l) with Russian leader Vladimir Putin (Photo: kremlin.ru)

"The 2019 elections are especially important," they said in an open letter published on Thursday (9 May).

"That's why we, the heads of state ... appeal to all those European citizens entitled to vote to take part in the European Parliament elections," the 21 presidents added.

They warned that "for the first time since the start of European integration, there are voices calling for steps backward in that process, whether on freedom of movement, or the abolition of joint institutions".

They also warned that some trends, such as deeper eurozone integration, could lead to "a Europe of various speeds".

The letter praised the EU in grandiloquent terms.

They called it the "realisation of a centuries-old dream of peace in Europe" and a project "without precedent in European history".

They pledged allegiance to EU values of "freedom, equality, solidarity, democracy, justice, and loyalty".

They said that only a "strong EU" could tackle challenges such as climate change, terrorism, global trade shifts, and migration.

They also repeatedly attacked nationalism.

"Nationalism and other extreme ideologies led Europe to the barbarity of two world wars," they said.

Young Europeans "no longer felt any contradiction between the love of their own village, town, region, or country, and the posture of an engaged European," the letter noted.

"There can be no return to a Europe of countries opposed to one another," it added.

The letter was signed by the presidents of Austria, Bulgaria, Croatia, the Czech Republic, Cyprus, Estonia, Finland, France, Germany, Greece, Hungary, Ireland, Italy, Latvia, Lithuania, Malta, Poland, Portugal, Romania, Slovakia, and Slovenia.

The seven other EU countries - Belgium, Denmark, Luxembourg, the Netherlands, Spain, Sweden, and the UK - have aristocrats instead of politicians as heads of state.

The letter came out as EU leaders meet in Sibiu, Romania, to ponder the bloc's future in the wake of Brexit.

It also came after 40 years of steadily falling turnout in the EP vote.

Some 62 percent of voters took part in the first ever elections in 1979, compared to fewer than 43 percent the last time around in 2014.

The figure in some blackspots was even lower, with just 13 percent of Slovaks and 18 percent of Czechs taking part five years ago.

Low turnout often favoured radical candidates, whose supporters tended to be more highly motivated than those of mainstream ones.

At the same time, nationalist and populist parties are polling to do better than ever in countries including Austria, France, Germany, Hungary, Italy, and Poland.

The pro-European views of the presidents of Austria, Hungary, and Italy stand in contrast to those of the hard-right parties in government in Budapest, Rome, and Vienna, even if the heads of state have purely ceremonial roles.

The signatures of Czech president Milos Zeman, a Russophile eurosceptic, and Poland's Andrzej Duda, a creature of the ruling and eurosceptic Law and Justice party, were more surprising, however.

The EU was an "imaginary community from which we don't gain much", Duda said at a rally last September.

Thursday's letter noted that there were "different views" among EU citizens and leaders on key issues, such as migration.

It also said there was "room in Europe for a wide range of ideas and opinions".

But it added that: "Despite this, we can all agree, that European integration and unity are essential issues and that we want to continue to realise the idea of Europe as a union".