Russian officials have said a US decision to supply weapons to Ukraine is dangerous and will encourage Kiev to use force in eastern Ukraine.
The US state department said on Friday the United States will provide Ukraine with "enhanced defensive capabilities" as the country battles Russian-backed separatists in the east.
Russia's RIA state news agency quoted Deputy Foreign Minister Grigory Karasin as saying on Saturday that supplies of any weapons would encourage those who support the conflict in eastern Ukraine to use the "force scenario".
Franz Klintsevich, a member of the upper house of the Russian parliament's security committee, said Ukraine would consider arms deliveries as support of its actions, Interfax news agency reported.
"Americans, in fact, directly push Ukrainian forces to war," Klintsevich said.
The war in eastern Ukraine between pro-Russian separatists and Ukrainian government forces has killed more than 10,000 people and displaced 1.7 million people in three years.
Michael Bociurkiw, former spokesman for the Organization for Security and Co-operation in Europe, told Al Jazeera that between January and November this year the conflict has resulted in at least 450 civilian casualties.
"There are millions of people in the conflict zone that are affected day in and day out, and recently a lot of schools, hospitals and other places where civilians gather have been shelled," he said.
Kiev accuses Moscow of sending troops and heavy weapons to the region, which Russia denies.
The US move deepens American involvement in the conflict and potentially further strains Washington's relations with Moscow.
According to sources quoted by The Associated Press, the new weapons, if approved by the US Congress, include American-made Javelin anti-tank missiles that Ukraine has long sought to boost its defences against the rebels, who have rolled through eastern Ukraine in tanks since 2014.
But military analyst Steven Fish said the defence package is not going to have a major impact in the conflict.
"The truth is that this is not a game changer on the ground in Ukraine," he said.
"What's been promised now really are just sniper rifles. This is not going to change things on the ground and Moscow knows that - this is not striking fear in the heart of anybody in the defence ministry in Moscow."
Previously, the US provided Ukraine with support equipment and training, and has let private companies sell small arms.
In a statement late on Friday, US state department spokeswoman Heather Nauert said the "enhanced defensive capabilities" would help Ukraine build its military long-term, defend its sovereignty and "deter further aggression".
The Russian foreign ministry said the US decision undermines Minsk agreements, TASS state news agency reported on Saturday.