Russia's renewed offensive in Ukraine raises World War Three fears.The news comes as Russian President Vladimir Putin looks to have increased attacks with troops launching a horrific attack on a shopping centre containing around 1,000 people.Alliance Secretary-General Jens Stoltenberg revealed the huge boost from coalition’s existing response force, as NATO leaders prepare to descend on Madrid for a crunch summit tomorrow (June 28).READ MORE: Russia promoting 'Siberian staycation' to Putin's personal hotspots following flight banSpeaking at a press conference at NATO headquarters in Brussels, Mr Stoltenberg pledged a "fundamental shift in NATO’s deterrence and defence".He said: "We will transform the NATO response force and increase the number of our high readiness forces to well over 300,000.”With countries fearing mounting aggression from Moscow following Vladimir Putin’s war on Russia's neighbour, the measure is designed at bolstering defences where Baltic states border Russia.