By Tom Esslemont
BBC News, South Caucasus correspondent
Azerbaijan is marking the 20th anniversary of the day when Soviet troops fired on the citizens of its capital, Baku, killing 137 people.
The dead, and 600 who were wounded, are being remembered in a national holiday.
Now known as Martyrs' Day, 20 January became etched into the minds of Azeris as one of the country's bloodiest.
The heavy-handed tactics were condemned by members of the Soviet establishment and marked the beginning of the end of Soviet rule in the country.
January 1990 was a pivotal month in the Azeri struggle for independence.
As the Soviet Union began to collapse from the inside, the Caucasian states began to tear away from Moscow's rule.
Clashes between Armenians and Azeris had already started in the mountainous region of Nagorno Karabakh - a territory which is still in dispute.
The Soviet army was sent in with the aim of ending clashes and to put down a separatist insurrection by Azeri nationalists.
It did not work.
The sound of gunfire could be heard across Baku and soon a military curfew was imposed.
It was yet another crisis for the embattled Soviet President Mikhail Gorbachev to deal with.
Territorial warfare between Christian Armenians and mainly Muslim Azerbaijan raged for a further four years.