Russian President Vladimir Putin has warned that Moscow could arm countries with a view to attacking Western targets.
Mr Putin made the statement while criticising the West’s delivery of long-range weapons to Ukraine.
Several countries including the United States have given Ukraine the green light to strike targets inside Russia.
Such action could lead to “very serious problems”, Mr Putin told foreign reporters.
“If someone thinks it is possible to supply such weapons to a war zone to attack our territory and create problems for us, why don’t we have the right to supply weapons of the same class to regions of the world where there will be strikes on sensitive facilities of those countries?” the Russian president said.
“That is, the response can be asymmetric. We will think about it.”
He did not specify which countries Moscow could supply weapons to.
Mr Putin singled out Germany, which recently told Ukraine it was free to hit targets inside Russia with long-range German-made weapons.
“When they say that there will be more missiles which will hit targets on Russian territory, this definitively destroys Russian-German relations,” Mr Putin said.
US President Joe Biden has given Ukraine permission to use American-supplied weapons to strike targets in Russia, but only near the Kharkiv region. The White House has said Ukraine cannot use long-range ATACMS missiles on Russian soil.
Ukraine has used US weapons to strike inside Russia in recent days, a US senator and a Western official told the Associated Press on Wednesday.
Fierce fighting has been raging north-east of Kharkiv since a new Russian push across Ukraine’s northern border. Kharkiv, Ukraine’s second city, is just 30km (18 miles) from the border.
UK Foreign Secretary Lord Cameron has said it is up to Ukraine to decide how to use British weapons and insisted it has the right to strike targets on Russian territory.
Ukraine says North Korean missiles are being used inside Ukrainian territory, and Western intelligence agencies say Russia has been using Iranian-made drones in the conflict.