"The construction of a European union of countries, people and nations ... can become permanent not on the basis of a joint economy and foreign policy, but mainly on the basis of spiritual unity, common values," he said in his homily.

"I hope that in our societies people's hearts and minds, which see the solution of economic problems differently, find a harmony of understanding, which today becomes a reality in our prayers and worries about a united Europe," he added after the eucharist.

For his part, Cardinal Kazimierz Nycz, the most senior priest in Warsaw, urged "everybody to take part in a great prayer for Europe."

The language of divine intervention is exotic by the standards of secularist EU countries. But it comes amid fears in Poland, where catholic tradition resonates deeply, that the collapse of the euro and the EU would put the country in danger and could even lead to military conflicts.

Meanwhile, Kowalski's endorsement of the Polish EU presidency is likely to pay dividends in upcoming elections on 9 October.

The ruling centre-right Civic Platform party has put its EU chairmanship at the heart of its campaign. The Polish church has in the past backed the more conservative Law and Justice opposition party. But Law and Justice's biggest church allies these days are fringe characters, such as far-right radio-evangelist Tadeusz Rydzyk.

"We commend unto God in our prayers ... the Polish presidency in the EU Council," Kowalczyk said. "It is a great undertaking, challenge and opportunity for our executive powers, and standing beside them, our whole society."

No senior Law and Justice people went to the Civic Platform mass on Sunday. The event was the third of its kind since July.