Commemorations are underway in Kyiv to honor the victims of deadly clashes between antigovernment protesters and security forces a year ago.

The violence killed more than 100 people, including 17 security officers, between February 18 and 21, 2014.

Another nine participants in Kyiv's Euromaidan protests died in the weeks that preceded the clashes.

The revolt led to the ouster of President Viktor Yanukovych, who has since fled to Russia. He says his overthrow was illegal and has denounced Ukraine's new leadership as "fascists."

His elected successor, President Petro Poroshenko, has designated February 20, the day most of the victims lost their lives, as an official day of remembrance.

Hundreds of people marched in Kyiv to honor their memory, and mourners laid flowers and candles at sites where protesters were shot dead.

A religious service was held in Independence Square, where the protests took place.

Another religious service took place at a church situated in a nearby street that saw some of the worst bloodshed.

Poroshenko is due to address the nation later in the day from Independence Square.

Church bells will ring across the country and a minute of silence will be held.

A concert on the square will wrap up the commemorations, with poetry-reading and a choir singing the national anthem.

A dozen foreign leaders, including European Council President Donald Tusk, are expected to attend another memorial event in Kyiv on February 22.

Meanwhile, the head of Ukraine's Security Services has accused a Russian presidential aide of supervising a commando of Russian snipers believed to have targeted Euromaidan demonstrators.

Valentyn Nalyvaychenko told Ukraine's 1+1 television channel on February 20 that three groups of Russian Federal Security Service members visited Kyiv between November 2013 and February 2014 to organize efforts to disperse the protesters.

Nalyvaychenko said Vladislav Surkov, an influential aide of Russian President Vladimir Putin, was in charge of coordinating the operation.

With reporting by Interfax and TASS