WARSAW, Poland (AP) — Thousands of Poles marched through Warsaw on Saturday, waving European Union and Polish flags in a show of support for the troubled European project as leaders in Rome marked the 60th anniversary of its founding treaty.

The rally in Warsaw, which was held under the slogan "I Love You, Europe," was also a strong expression of disapproval for the nationalist and Euroskeptic government in Warsaw, which was recently involved in a bitter standoff with the bloc.

Thousands of people began their demonstration by singing European anthem "Ode to Joy" followed by the Polish national anthem before marching to the Royal Castle in historic town center.

Government critics fear that the government policies could ultimately result in Poland leaving the EU.

"We will not let ourselves be led out of Europe," Ryszard Petru, the head of the opposition Modern party, told those gathered.

He also said that the ruling Law and Justice party's stance on Europe doesn't reflect the will of the nation, which is overwhelmingly pro-EU. Recent opinion polls put support for the EU by Poles at around 80 percent.

The Polish government denies that leaving the EU is its aim and insists that it instead simply wants reforms and wants to keep the bulk of power with national governments, not in Brussels.

The recent tensions centered around stiff opposition by the conservative Polish government to the re-election of Donald Tusk, a former Polish prime minister, as head of the European Council. Tusk has long been a bitter political rival of Jaroslaw Kaczynski, the head of the ruling Law and Justice party and the most powerful politician in Poland.

Before the EU meeting in Rome, Polish Prime Minister Beata Szydlo had also threatened not to endorse the declaration. But on the eve of the summit she backed away from the position and signed it on Saturday.