Russian President Vladimir Putin has said that any decision by the United States to supply lethal weapons to Ukraine would fuel the conflict in the country's east.
Putin told journalists on September 5 after a BRICS summit in China that it was up to Washington to decide whom it sold or gave weapons to, but that delivering weapons to a conflict zone "doesn't help peacekeeping efforts, but only worsens the situation."
U.S. Defense Secretary Jim Mattis said last month that Washington was "actively reviewing" supplying Ukraine with lethal defensive weaponry to help it defend itself from Russia-backed separatists in the eastern regions of Donetsk and Luhansk.
"Such a decision would not change the situation but the number of casualties could increase," said Putin, who suggested that the separatists could to respond by expanding their own campaign.
"The self-proclaimed republics have enough weapons, including those they have seized from the opposite side," the Russian president said, referring to the separatists as self-proclaimed republics.
"It is hard to say how the self-proclaimed republics may react to the supply of U.S. weapons to the conflict zone," he said. "They might deploy weapons to other areas of the conflict that are sensitive for those who create problems for them."
Kyiv and NATO say Russia has supplied many of the weapons used by the separatists, and Putin's remark was widely interpreted as a warning that Russia and the separatists could respond by beefing up their firepower, increasing pressure on government forces, and trying to seize additional land in Ukraine.
Russia and the West are at deeply at odds over Russia's armed takeover of Ukraine's Crimea region in March 2014 and its backing of the separatists in the conflict that has killed more than 10,000 people in eastern Ukraine since April 2014.
Visiting Kyiv on August 24, the 26th anniversary of Ukraine's declaration of independence from the Soviet Union, Mattis said, "On the defensive lethal weapons, we are actively reviewing it."
He added that he would inform Secretary of State Rex Tillerson and President Donald Trump about his position on the issue "in very specific terms."
"Defensive weapons are not provocative unless you are an aggressor, and clearly Ukraine is not an aggressor since it is their own territory where the fighting is happening," Mattis said, appearing to signal support for Kyiv's request for defensive weaponry.
Russian officials and separatist leaders criticized Washington and Kyiv for discussing the provision of lethal weapons and rejected the assertion that doing so would not be "provocative."
U.S. media reported on August 6 that the Pentagon had recommended sending a package of lethal defensive military aid to Ukraine worth about $50 million.
The weapons package would reportedly include Javelin shoulder-launched antitank missiles, which Kyiv has long sought to defend against the Russia-backed forces it has been fighting in its east for more than three years.
Putin also supported on September 5 the idea of deploying an international force to eastern Ukraine to help protect monitors observing the conflict, saying such a deployment would be "completely appropriate."
He said Moscow intended to draft a UN Security Council resolution on deploying the force, saying it would "help resolve the problem in eastern Ukraine."
Putin cautioned that a number of preconditions would need to be met before any such deployment happened.
He insisted that the force should only ensure the security of the unarmed mission from the Organization for Security and Cooperation in Europe (OSCE) and be restricted to operating on the "demarcation line" between Ukrainian forces and the separatists.
The Ukrainian Foreign Ministry said Kyiv was "prepared to work on this issue."
A statement said the Ukrainian mission in New York "has been instructed to hold relevant consultations with delegations at the UN Security Council."
Ukraine has long called for the deployment of UN peacekeepers in separatist-held territory but has said that they should be deployed throughout the area, including along the part of the Ukraine-Russia border that Kyiv does not currently control.
Kyiv is concerned that deploying peacekeepers along the demarcation line only would cement the separatists' control over they territory they hold and leave Russia free to sends troops and weapons across the international border.