Turkish President Recep Tayyip Erdogan has pledged at a commemoration of a World War I campaign to "keep on standing firm" despite forces against him before a constitutional referendum next month on whether to expand president's powers in Turkey.

Speaking in the Aegean port of Canakkale, near where Ottoman armies held off an Allied expeditionary force in 1915-1916, Erdogan criticised some European countries that have prevented Turkish ministers from campaigning for votes in the Turkish diaspora.

"Let them try and hinder them. Whether Germans, Dutch, Austrians, Swiss, Belgians, Danes or whoever it is, know that your president has stood firm and will keep on standing firm," he said.

He maintained that an executive presidency and the abolition of the prime minister's post would help Turkey develop economically and deal with security challenges, which included a botched coup attempt last year.

Opponents of the democratically elected president view the April 16 referendum as part of a dangerous drift towards authoritarian rule.

Speaking in Ankara, Turkey's main opposition leader, Kemal Kilicdaroglu, urged Turks to vote no in the referendum, saying approval would undermine democracy.

Supporters see him as a pillar of stability, Muslim piety and nationalist pride in a turbulent region that includes neighbouring Syria.

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The March 18 anniversary marks the beginning of an Allied naval bombardment near Canakkale, at the Dardanelles strait.

The Canakkale battle is referred to by its former Allied adversaries, including Australia and New Zealand, as the Gallipoli campaign.

Former Allied nations hold their own commemoration on April 25, the day in 1915 when troops under British command landed after the bombardment.

The Allied force failed to advance and withdrew in early 1916.

Source: News agencies