Ukraine's increasingly effective long-range drone campaign is piling pressure on Vladimir Putin, striking at the heart of Russia's oil industry, embarrassing the Kremlin on the world stage and compounding a growing list of military and economic setbacks. The latest blow came on Wednesday when Ukraine staged a massive attack on a major oil port in St Petersburg just hours before the opening of Putin's flagship international investment summit.The oil terminal on the Gulf of Finland is one of Russia's largest fuel storage and export facilities, handling 12.5 million tonnes of fuel annually. The strike occurred shortly before the St Petersburg International Economic Forum, known as 'Russia's Davos', where Putin seeks to project economic strength and international relevance despite Western sanctions and the war in Ukraine.The attack made a mockery of the forum's theme, 'Pragmatic dialogue - the path to a stable future', while also exposing glaring weaknesses in Russian air defences. The facility is located just 12 miles from the forum venue, yet Moscow failed to prevent the strike.It is the latest in a string of successful Ukrainian long-range attacks that have increasingly targeted the infrastructure underpinning Russia's war effort.Over recent months, Kyiv has repeatedly struck refineries, oil terminals, pumping stations and export facilities deep inside Russian territory.