US Vice President Joe Biden has warned that Russia faces “rising costs and greater isolation” if it fails to respect peace deals in Ukraine.
Mr Biden, on a visit to Ukraine, said Russia continued to violate ceasefires.
He was speaking after holding talks with President Petro Poroshenko.
Some 4,300 people are thought to have died in eastern Ukraine’s conflict since April. Russia is regularly accused of arming separatist rebels, but its officials deny the allegations.
Mr Biden is in Kiev on the first anniversary of the start of mass protests that culminated in President Viktor Yanukovych relinquishing power.
An appeal on social media is credited by many with starting the wave of protests one year ago which ended in the overthrow of President Viktor Yanukovych.
Mustafa Nayyem, a Ukrainian investigative journalist of Afghan origin, asked people on Twitter and Facebook to spread his call to meet that night on Independence Square – the space at the heart of the Ukrainian capital affectionately known as the Maidan (“square” in Ukrainian).
