U.S. Vice President Joe Biden has condemned what he calls Russian "aggression" after meeting with Ukrainian President Petro Poroshenko and Prime Minister Arseniy Yatsenyuk in Kyiv.
Biden said they talked about the threat to Ukrainian sovereignty and territorial integrity posed by Russia's military intervention. He called Russia's annexation of Crimea and its backing for separatists in the east a "flagrant violation of the bedrock principles of the international system."
Biden also accused Russia of ignoring the September cease-fire between Ukraine and pro-Russian separatists.
The United Nations says nearly 1,000 people have been killed since the cease-fire took. Both sides blame the other for violating the truce.
Meanwhile, a U.S. cargo plane delivered three radar units for the Ukrainian military. Twenty units to detect incoming mortar fire will be sent to Ukraine over the next few weeks.
U.S. President Barack Obama has ruled out sending weapons to Ukraine, restricting help to non-lethal aid such as body armor, radios and vehicles.
Ukraine has appealed for arms and U.S. Deputy National Security Advisor Tony Blinken told Congress during the week that arming Ukraine could cause Russia to rethink its role there.
Russia has warned that sending weapons to Ukrainian troops would seriously destabilize the situation.
The West has accused Russia of directly sending weapons and forces into Ukraine -- a charge Russia denies.
Friday was the first anniversary of the popular uprising in Ukraine that forced pro-Russian President Viktor Yanukovych to flee after unexpectedly backing out of an economic deal with the European Union.
The uprising in Kyiv prompted Russian speakers in eastern Ukraine to defend themselves against what they saw as a threat by the new pro-Western leadership. This led to Russia's annexation of the Crimean peninsula.
Some material for this report came from Reuters