People march in downtown Kiev on Sunday, Feb. 22, 2015. In Kiev, thousands participated in a march on Sunday commemorating the events of a year ago and honoring the more than 100 protesters who died during them. President Petro Poroshenko led the ceremony, joined by foreign representatives including the presidents of Poland, Lithuania, Germany, Georgia and the European Union. (Sergei Chuzavkov/AP)

A bomb killed two people Sunday at a march in the city of Kharkiv commemorating the first anniversary of the ouster of former president Viktor Yanu­kovych, and Ukrainian officials said Russia was behind the attack.

Yanukovych had enjoyed the Kremlin’s favor, and when he fled from Kiev a year ago in the face of the huge protests on the Maidan, or Independence Square, that set in motion Moscow’s seizure of Crimea and the beginning of the separatist fighting in the eastern part of the country.

The attack is the latest in a string of bombings in Kharkiv over the past few months, including explosions outside a courthouse that injured 14 last month, outside a national guard outpost, near a military hospital and at a bar frequented by Kiev supporters. Kharkiv is about 90 miles northwest of the borders of the Donetsk and Luhansk regions, which pro-Russian separatists are seeking to claim as republics independent from Kiev. It was where Yanukovych made a brief stop on his flight into exile in Russia.

Ukrainian officials called the bombing an act of terrorism.

Markian Lubkivskyi, a spokesman for the national Security Service, said that the alleged perpetrators of Sunday’s bombing had been trained in Russia and that their bomb had been made in Russia.

The Kremlin did not comment on the Kharkiv attack Sunday, but in the past, Russia has denied any direct involvement in the Ukraine conflict.

The attack came as Ukrainian and separatist leaders announced they would begin pulling back their heavy weapons from the front line, as required by a key component of the cease-fire agreement struck in Minsk nearly two weeks ago. The cease-fire’s efficacy has been in doubt since it was signed, as fighting in the area of Debaltseve only increased in the days after the agreement was struck. Pro-Kiev forces retreated from the city last week.

Pro-Russian rebels and the Ukrainian military also swapped prisoners Saturday, an event officials on both sides of the conflict suggested could be followed by another exchange soon.

But military officials in Mariupol, a strategic port on the Sea of Azov, reported Sunday that rebels had launched an offensive to the east of the city.

Meanwhile, European leaders appeared with Ukrainian President Petro Poroshenko at events commemorating the Maidan anniversary in Kiev on Sunday, where the European Council president, Donald Tusk, suggested that Europe would soon revisit the subject of broadening economic sanctions against Russia.