ANKARA, Turkey (AP) — Police on Monday used tear gas and water cannons to try to break up a demonstration by tens of thousands of pro-secular protesters, but the march to mark the founding of the Turkish republic went on in defiance of a government ban.

The Republic Day celebrations have in the past few years become a symbol of the divide between Prime Minister Recep Tayyip Erdogan’s elected, Islamic-leaning government and its opponents who fear the country’s secular traditions are in danger.

The Ankara governor’s office last week denied authorization for the march, citing security reasons, and declared the gathering illegal.

Challenging the ban, tens of thousands of people assembled in the old part of Ankara, near the building housing Turkey’s first parliament, to march to the mausoleum of Mustafa Kemal Ataturk, who founded the secular republic 89 years ago after the collapse of the Ottoman Empire.

Police tried to disperse the crowds before a barricade was lifted and the protesters proceeded to march, waving Turkish flags and carrying posters of Ataturk.

They chanted: "We are the soldiers of Mustafa Kemal!" and "Turkey is secular and will remain secular!"

The march was supported by the main opposition party, whose leader Kemal Kilicdaroglu was among those affected by the gas.

Media reports and opposition politicians said police earlier prevented buses carrying some demonstrators from traveling to Ankara to take part in the march.