MOSCOW/KYIV - Ukraine's security cannot be addressed without considering Russia's security, Russian President Vladimir Putin said on Friday.

"Despite the fact that each country has the right to choose how to ensure its own security, such issues cannot be resolved without regard for Russia's own security," Putin said when answering questions at the plenary session of the Eastern Economic Forum (EEF).

The Russian leader warned that any foreign troops in Ukraine would be legitimate targets for the Russian army.

Speaking about potential contacts with Ukrainian President Volodymyr Zelensky, Putin said that "it will be practically impossible" to reach agreements with Ukraine on key issues.

"Even if there is political will -- which I doubt -- there are legal and technical difficulties," he said.

Following his China visit, Putin traveled to Russia's far eastern port city of Vladivostok to attend the 10th EEF, which ends on Saturday. 

Ryazan oil refinery

Separately, the Unmanned Systems Forces (USF) of the Ukrainian Armed Forces said Friday that they had struck the Ryazan oil refinery in western Russia overnight.

In a statement on Telegram, the USF described the refinery as a strategic energy facility with an annual processing capacity of 17.1 million tons of oil or 6.1 percent of Russia's total refining volume.

The strike sparked a fire at the refinery, and the extent of the damage is being assessed, the statement said.

The USF also reported hitting an oil depot in the city of Luhansk, which is currently under Russia's control, triggering explosions.