World Bulletin/News Desk
Both sides have also accused each other of violating the ceasefire and Ukraine said on Friday that its territory had come under cross-border artillery fire from inside Russia for the first time since the truce came into force.
Biden's visit to Kiev took place on the first anniversary of the decision by the government of Ukraine's then president Viktor Yanukovich to ditch a political and trade pact with the European Union in favour of renewed ties with Russia.
The move provoked protests from tens of thousands of Ukrainians and led to the ousting of the Moscow-backed Yanukovich. It triggered the worst confrontation between Russia and the West since the Cold War after Russia annexed Crimea in March and backed the eastern separatists.
Tensions still simmering in Ukraine's war-wracked society came to the surface on Friday when Poroshenko went to pay tribute to the 100 or so protesters who were killed in February by police snipers before Yanukovich fled.
Relatives of those killed, frustrated by the government's failure to bring officials of the Yanukovich government to book, shouted, "Where are their killers?" and "Down with Poroshenko!"
They also attacked him for failing to keep a promise to confer the title of national hero on the victims, which would bring financial benefits to the families of those killed.
Poroshenko later returned to the scene to pledge that he would sign a decree to officially designate the victims, known as the "Heaven's Hundred", as national heroes as promised.
Biden, appearing alongside Poroshenko, said Russia's annexation of the Crimea and backing for the separatists represented a "flagrant violation of the bedrock principles of the international system."Last Mod: 21 Kasım 2014, 17:32