When Ukraine cuts off Russian gas shipments via its pipelines, the European Union will face major shortages – but few as bad as in tiny Moldova.
UK intelligence say Putin's forces are attacking "behind established Ukrainian defences".
Trump "is intelligent and I hope he’s cautious and understands this,” the Russian leader said.
The Russian president also used the opportunity to praise "intelligent" Donald Trump.
Russia's acts of sabotage could trigger the "mutual defence clause" of the alliance.