Russia's foreign ministry said on Monday that those supplying lethal weapons to Ukraine will bear responsibility should they be used during Russia's military campaign there.
The ministry added that the steps the European Union has taken against Russia will not be left without a harsh response.
Earlier Monday, British Prime Minister Boris Johnson told leaders of countries including the United States, France and Germany in a call to continue supplying weapons to Ukraine, a government spokesperson said.
Johnson was joined on the call with other world leaders and representatives of the European Union and NATO.
"The prime minister stressed the need for countries to continue supporting the Ukrainian government, including with the provision of defensive weapons," the government spokesperson said.
"The prime minister welcomed the unity of message and action between countries in recent days in response to Russia's invasion. He stressed the need to continue applying pressure on Putin's regime, including on SWIFT, with sanctions and with trade restrictions."
Meanwhile, Canadian Prime Minister Justin Trudeau said his country will supply anti-tank weapons and upgraded ammunition to Ukraine to support its fight against the Russians as well as ban imports of crude oil from Russia.
"Canada will continue to deliver support for Ukraine's heroic defense against the Russian military," Trudeau told reporters in Ottawa. "We are announcing our intention to ban all imports of crude oil from Russia, an industry that has benefited President Putin and his oligarchs greatly."
Canada imported C$289 million worth of energy products in 2021, according to Statistics Canada.
Canada has already sent weapons and non-lethal support to Ukraine, and it has backed a number of sanctions, including supporting the removal of Russia from the SWIFT system for international bank payments.
Canada also played a role in restricting Russia's central bank from being able to access its foreign reserves.
Earlier on Monday, Foreign Minister Melanie Joly said the G7 would bring more sanctions against Russia.
They join a host of Western countries that have already mobilized to supply Ukraine with weapons in an attempt to fend off the Russian invasion, the biggest attack on a European state since World War Two, including Sweden, Denmark and Germany.