Amid tight security, demonstrators including MPs of Armenian origin blocked a main highway leading into Beirut, waving Armenian flags and carrying banners that read: "1,500,000 Armenians massacred, but we survived. We'll tell you the history of Turkey's atrocities."
Other banners read: "Run, Turkey, run, but you can't hide," and "Impunity nurtures culture devoid of ethics."
Armenians say up to 1.5 million of their kin were systematically killed between 1915 and 1917 as the Ottoman Empire, the predecessor of modern Turkey, was falling apart.
The events are marked every year on April 24, the date in 1915 when Ottoman authorities rounded up and arrested more than 200 Armenian intellectuals and community leaders in Constantinople.
Turkey fiercely rejects the genocide label, arguing instead that between 300,000 and 500,000 Armenians and at least as many Turks died in civil strife when Armenians took up arms in eastern Anatolia and sided with invading Russian troops.
The dispute has poisoned relations between the two neighbours for decades, and reconciliation efforts launched last year remain frozen.
Hundreds of thousands of Armenian Christians are believed to have fled to Lebanon after the mass killings.
Lebanon today hosts the Arab world's largest Armenian community, estimated at around 140,000 people.
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