President Vladimir Putin warned on June 5 that Russia could provide long-range weapons to other countries to attack Western targets because NATO allies were allowing Ukraine to use its weapons to attack Russian territory.

Mr Putin also reiterated that Moscow was ready to use nuclear weapons if it saw any threat to its sovereignty.

He responded to questions from international journalists, saying the West’s recent actions would further undermine international security and could cause “very serious problems” — something that has become increasingly rare since Moscow sent troops into Ukraine.

“This would mark their direct participation in a war against the Russian Federation, and we reserve the right to act accordingly,” Mr Putin said.

The United States and Germany have recently authorised Ukraine to attack certain targets on Russian soil, for which they are supplying long-range weapons to Kiev.

On Wednesday, a Western official and a U.S. senator said Ukraine had used U.S. weapons to strike inside Russia under newly approved guidance from President Joe Biden that allows U.S. weapons to be used for the limited purpose of defending Kharkiv, Ukraine’s second-largest city. The official was not authorized to comment publicly on the sensitive matter and spoke on condition of anonymity.

Mr Putin claimed that the use of some weapons supplied by Western countries involves those countries’ military personnel controlling the missiles and choosing targets, and so he said Moscow could take “asymmetric” steps in other parts of the world. The US military said it does not control the missiles or targets supplied to Ukraine.

“If they find it possible to deliver such weapons to a war zone in order to attack our territory and create problems for us, why don’t we have the right to supply the same type of weapons to certain regions of the world where they could be used to attack sensitive facilities of countries that are attacking Russia?” he said.

“We will think about it,” he told reporters on the sidelines of the annual St. Petersburg International Economic Forum.

Asked whether Russia could use nuclear weapons, Putin said the conditions for using the arsenal were clearly spelled out in Moscow’s security doctrine.

“For some reason, there is a belief in the West that Russia will never use it,” he said.

“Look at what’s written there,” he said of Russia’s nuclear doctrine. “If someone’s actions threaten our sovereignty and territorial integrity, we consider it possible to use all means at our disposal.”

Putin said even Russia’s battlefield nuclear weapons are far more powerful than those used by the United States against Japan in World War II.

Speaking for more than three hours to senior news leaders from international news agencies, including the Associated Press, Putin also said that nothing would change in terms of Russia-US relations regardless of the victory of Biden or Donald Trump in the US presidential election in November.

“We will work with any president elected by the American people,” Putin said.

“I’ll be honest, I wouldn’t say we believe there will be any change in Russia’s track record in American politics after the election,” he said. “We don’t think so. We think nothing serious will happen.”

Mr Putin also said Trump’s conviction last week in a hush-money money trial was the result of “the use of the court system as part of an internal political struggle”.

The Russian leader faced questions on a variety of topics, although the issue of the fighting that has been going on for more than two years in Ukraine dominated the session.

Mr Putin claimed the West had opportunities to end the fighting in Ukraine but did not act on them. He cited a letter he reportedly wrote to Biden, which said hostilities could end in two or three months if Washington stopped supplying arms to Kiev.

Asked about Russian military losses, Mr Putin said no country would reveal this information during hostilities, but claimed, without giving details, that Ukraine’s casualties were five times higher than Russia’s.

He also said that more than 1,300 Russian soldiers were held captive in Ukraine, while more than 6,400 Ukrainian soldiers were held in Russia.

These claims could not be independently confirmed and some Western estimates put Russia’s losses far higher than Ukraine’s.

Asked by AP about the case of Wall Street Journal reporter Ivan Gershkovich, Putin said the U.S. was “taking all-out measures” to ensure his release. Gershkovich was jailed a year ago during a reporting trip and accused of espionage. The journalist, his employer and the U.S. have denied the charges, and Washington has said he has been wrongly detained.

Mr Putin said the decision on any such release is “not taken through the mass media” but through a “prudent, sober and professional approach”.

“And of course these must only be decided on the basis of reciprocity,” he added, pointing to possible prisoner swaps.

Mr Putin has used the St Petersburg forum to promote Russia’s development and seek investors. The meeting with reporters took place at Gazprom’s new global headquarters, a needle-shaped 81-storey skyscraper rising above the Gulf of Finland.

Although meetings with reporters were part of previous sessions, he has not answered questions from Western reporters at the St. Petersburg event since sending troops to Ukraine.

Last year, journalists from countries Russia considers unfriendly, including the United States, Britain and the European Union, were not invited, and Western officials and investors also did not attend the session after sweeping sanctions were imposed on Moscow over Ukraine.