A dispute over a Russian fighter jet’s interception of a US spy plane flying towards Russia’s border last week has underscored the mounting war tensions sparked by the US-NATO buildup in eastern Europe.

Washington has denounced the April 7 interception, with the Pentagon claiming that it was “unsafe and unprofessional.” Pentagon spokesman Mark Wright warned that “the careless actions of a single pilot have the potential to escalate tensions between countries.”

The US European Command announced on Saturday that it would file a formal complaint over the incident.

Moscow refuted the accusations. Maj. Gen. Igor Konashenkov said that a Russian SU-27 fighter jet was scrambled after an unidentified airborne object was spotted over the Baltic Sea north of Poland headed directly toward Russian territory. The fighter pilot ascertained that the airborne target was a US RC-135U, a large reconnaissance aircraft, which was flying with its transponder turned off, concealing its identity.

“I want to emphasize that the RC-135U was moving toward the Russian border with its transponder switched off,” said the Russian general. “As to the professional qualities of our pilots, this is something for the Russian military to assess. Moreover, US reconnaissance planes are supposed to fly along US borders and nowhere else.”

The aerial confrontation was only one of an increasing number as the US and its NATO allies stage nearly continuous and confrontational exercises near the Russian border. The spy flights, which are apparently targeting Baltic Sea military bases in Kaliningrad, the Russian territory wedged between Poland and Lithuania, have particularly ratcheted up tensions.

In a separate incident on Tuesday, London’s Ministry of Defense reported the scrambling of Typhoon fighter planes to intercept two Russian TU-95 “Bear” strategic bombers “flying close to British airspace.” The statement provided no precise location for the interception.

A spokesman for the Russian Defense Ministry insisted that the Russian aircraft had “operated in absolute compliance with international rules and did not violate anything.”

The incident followed a statement made Sunday by a Pentagon spokesman who charged that “The nature of Russian air activity is expanding west into Europe and becoming more aggressive.”

The aerial confrontations, charges and counter-charges recall some of the most tense periods of the Cold War between the US and the Soviet Union. With the aggressive deployment of US military forces within striking distance of Russia, however, the present confrontation is, if anything, considerably more dangerous.

The disputes over confrontations in the air came as US ground forces arrived in Ukraine last Friday to prepare six months of training and exercises involving US paratroopers of the 173rd Airborne Brigade and the Ukrainian National Guard, a force that includes paramilitary units that are funded by the country’s billionaire oligarchs and comprised of fascist and neo-Nazi volunteers.

Ukrainian officials have reported that at the end of the exercise, the US forces will hand over ammunition to the National Guard, representing the first direct provision of so-called lethal weaponry to Ukrainian military units.

Meanwhile, in Estonia, a squadron of US F-16 fighter jets is carrying out practice bombing runs within sight of the Russian border.

“Russia is so close that the F-16 fighter pilots can see it on the horizon as they swoop down over a training range in Estonia,” the Associated Press reported. “The simulated bombs release smoke on impact, but the M-61 cannon fires live ammunition, rattling the aircraft with a deafening tremor and shattering targets on the ground.”

The AP quoted Ian Kearns, director of the European Leadership Network, a London-based think tank, as warning, “If one commander or one pilot makes a mistake or a bad decision in this situation, we may have casualties and a high stakes cycle of escalation that is difficult to stop.”

As the AP itself notes, this “saber-rattling raises the specter that either side could misinterpret a move by the other, triggering a conflict between two powers with nuclear arsenals.”