NATO has been on high alert since Russia invaded Ukraine more than three and a half years ago, but a recent spike in the alliances airspace violations has security experts increasingly concerned that warnings of war with Moscow are no longer theoretical, but inevitable.President Donald Trump on Thursday said the U.S. could "end up in World War III" over Russias war in Ukraine and conceded that Russian President Vladimir Putin has "let him down" over his refusal to end his military campaign.One day later, Russia sent three fighter jets over Estonia's capital city of Tallinn in a direct and clear violation of its airspace, prompting another NATO member to spark Article 4 for the second time in as many weeks.RUSSIAN JETS VIOLATE ESTONIAN AIRSPACE, FOREIGN MINISTER SAYS"Russia is testing NATO again dozensof drones in Poland last week, drones in Lithuania, Latvia, Estonia, and now fighter jets in Estonian skies. These are deliberate provocations," Lithuanian Defense Minister Dovile Sakaliene told Fox News Digital. "They are deliberate teststests of our readiness, our resolve, and of the limits of our deterrence."Sakaliene said the Friday violation was just the latest in "an escalating pattern of pressure by Russia.""For Estonia, for Poland, for Lithuania, for all of NATOs eastern flank, this is a direct threatnot just to territorial integrity, but to citizen safety," she added.The Lithuanian defense minister warned that the biggest line of defense NATO holds right now, apart from its actual military readiness, is showing a united front to dissuade Moscow from taking direct action against a NATO member and prompting what could become a global war."Our biggest risk currently is miscalculation by Russia," Sakaliene said. "Does Russia believe that NATO will not allow violations of its territory? Does Russia believe that Europe is going to strike back together with [the] United States?"That's now the last line of defense between if and when [war with Russia happens]," she added.TRUMP AND ZELENSKYY TO MEET AS POLAND PRESSURES NATO ON NO FLY ZONE OVER UKRAINEConcern over direct NATO conflict with Moscow escalated earlier this month after a swarm of at least 19 Russian drones not only flew over Polish airspace, but forced a multi-nation response when NATO, for the first time since the war began, fired upon Russian assets and brought down as many as four drones that posed a threat.While Trump suggested that the drone swarm could have been a mistake, Poland refuted this and said it was "deliberate" and a "planned provocation."Drone strikes have long been a favored wartime tool of Russia's in its operation against Ukraine, with the number of strikes peaking in July with some 6,297 long-range drones fired across the country.That figure dipped to 4,216 drones fired in August. Though notably, the majority of those UAVs were fired between Aug. 16th and the 31st, when some 3,001 drones were deployed beginning the day after Trump met with Putin in Alaska on Aug. 15.An American company, which sat less than 30 miles from two other NATO nations, Hungary and Slovakia, was also hit with "several" cruise missiles in late August."The scope of air attacks from Russia to Ukraine is really rising. They are using more drones, more rockets, and they are still expected to rise," Sakaliene said."We have to admit and adapt to this new reality. High intensity war by Russia against Ukraine is ongoing," the defense minister said. "That means that more and more UAVs are going to wander off into the territories of the bordering countries, and even further."Russia has increasingly turned to gray-zone tactics, which involve incidents that fall below the threshold of open warfare, but which allow Russia to test NATOs resolve and response capabilities.Over the last month, Poland saw three separate incidents in which its airspace was violated by Russian drones, including UAVs carrying explosive components that crossed into its airspace from both Ukraine and Belarus.TRUMP DEMANDS NATO ALLIES HALT RUSSIAN OIL PURCHASES BEFORE NEW US SANCTIONSJust three days after the drone swarm bombarded Polish air defense systems, a Russian drone crossed into Romanian airspace and prompted a French fighter jet and Polish helicopter to respond under NATOs Operation Eastern Sentry a defensive posture the alliance launched just one day prior.These events came after Lithuania in late July was forced to sound the alarm following two separate incidents in which Russian Gerber drones violated its borders, including one which was carrying explosives.But these tactics are not the only threats that security experts in recent weeks have flagged as concerning behavior from Moscow.Earlier this month, the Institute for the Study of War (ISW) based in Washington, D.C. drew attention to an op-ed published by former Russian president and current Security Council chair Dmitry Medvedev on Sept. 8 in the state-sponsored news outlet TASS, which used language that directly mirrored rhetoric by the Kremlin in the lead up to its invasion of Ukraine.In his article, Medvedev accused Finland of being "Russophobic" and claimed, "the thirst for profit at the expense of Russia was installed in Finnish minds back in the days of Hitler."He further claimed that Helsinki has attempted to erase the "historical and cultural identity" of ethnic Russians and said joined NATO under the "guise" of defense, but in actuality, was covertly preparing for war against Russia, reported the ISW.Medvedevs comments were not stand-alone threats. Multiple Kremlin officials, including Putin who said "there will be problems" after Finland joined NATO, have claimed the alliance will use Finland as a "springboard" to attack Russia."Russia has been steadily setting conditions to attack NATO over the past several years: Moscow is standing up new divisions and optimizing its command and control headquarters on NATOs eastern flank," George Barros, Senior Russia Analyst with ISW told Fox News Digital. "The Kremlin information warfare apparatus is fabricating claims and justifications for why Finland, the Baltic States, and Poland are not real countries."These are the prerequisite preparations for future war that Moscow is preparing," he warned.Sakaliene echoed these concerns and additionally pointed to Russia's use of "soft power," often employed through social media and traditional media, to influence public perception, which she warned is "alarmingly effective."CLICK HERE TO GET THE FOX NEWS APP"We see a picture of a very aggressive country which is investing a disproportionate amount of its funds into their military capacity," the defense minister said. "Despite heavy losses every week, every month, they are moving forward in Ukraine, and at the same time, they are expanding their capabilities."It raises considerable doubts if all that mass of military power is being accumulated only for Ukraine," Sakaliene said.