Russian President Vladimir Putin has warned Western countries they're taking a "very serious and dangerous step" by supplying weapons to Ukraine, which could result in Moscow arming their enemies. Ukraine has relied heavily on arms supplied by Western allies to beat back Russian forces since Putin's full-scale invasion began more than two years ago. And last week, US President Joe Biden for the first time gave Kyiv permission to use American munitions to carry out limited strikes inside Russian territory, after several European nations removed restrictions on how weapons they supply can be used. "Supplying weapons to a conflict zone is always a bad thing," Putin told editors from international news agencies on the sidelines of the annual economic forum in St. Petersburg on Wednesday. "Especially if this is linked to the fact that those who supply them are not only delivering weapons but managing them." Putin also warned that Russia could retaliate if Western countries are deemed to have become directly involved in the Ukraine conflict. "In the end, if we see that these countries become involved in a war against us, what they are doing makes them directly involved in a war against the Russian Federation, we reserve the right to act the same way," he said. "Overall, it leads to some serious problems." And he raised the prospect of retaliatory action by asking why Russia would "not have the right to supply our weapons of the same class to those regions of the world where there will be strikes on the sensitive facilities of those countries that are doing this against Russia?" The Ukrainian military has started using US-supplied HIMARS rocket systems to hit Russian air defense systems, weapons depots and other military targets on Russian territory, a member of the Ukrainian Parliament told CNN on Wednesday. Yehor Cherniev, deputy chairman of the Ukrainian Parliament's Committee on National Security, Defense and Intelligence, said the American weapons had allowed them "to significantly reduce the shelling of Kharkiv by Russian S-300 missiles." In his comments Wednesday, Putin said Russia would improve air defense systems to destroy incoming missiles. He also singled out Berlin for criticism, following remarks last week from the leaders of France and Germany that Ukraine should be allowed to use their weapons against targets inside Russia from which Moscow attacks Ukraine. The appearance of German tanks in Ukraine had resulted in an "ethical shock" in Russia, where the attitude toward Germany had previously been "very good," Putin said. "Now, when they say that some more missiles will appear that will strike targets on Russian territory, this, of course, is ultimately destroying Russo-German relations," he added. Speaking alongside French President Emmanuel Macron on May 28, German Chancellor Olaf Scholz said Ukraine was allowed to defend itself as long as it respected the conditions given by the countries that supplied the weapons – including the United States – and international law. "Ukraine has every possibility under international law for what it is doing. That has to be said explicitly," Scholz said. "I find it strange when some people argue that it should not be allowed to defend itself and take measures that are suitable for this." Ukraine had for months pleaded with Washington to allow it to strike targets on Russian soil with US weapons, as Moscow launched a brutal aerial and ground assault on Kharkiv, knowing that its troops could retreat to Russian soil to regroup and its weapons depots could not be targeted with Western arms. The US is standing firm in not allowing Ukraine to use the most formidable munition it has been given to fire into Russia: the long-range missiles known as ATACMS that can hit targets 300 kilometers (nearly 200 miles) away. Instead, Ukraine can only use shorter-range missiles known as GMLRS, which have a range of around 70 kilometers (around 40 miles). — CNN