MOSCOW - A series of close encounters this month over the Baltic Sea and U.S. shoot-downs of Russian allies' aircraft in Syria have triggered concerns among defense analysts that any direct incident between Russia and the United States, even if accidental, could quickly spiral out of control.

Reports say a Russian fighter jet and a U.S. spy plane on Monday came within two meters of each other, a situation deemed "unsafe" by the U.S. military.

The Russian SU-27 flew at a high rate of closure speed and the pilot exercised poor control, said a Pentagon spokeswoman.

Risk of accidents

Russia's Defense Ministry said the U.S. RC-135 reconnaissance plane made a provocative move toward the other jet.

FILE - A Polish Air Force F-16 fighter jet flies n FILE - A Polish Air Force F-16 fighter jet flies near an airbase in Lask near Lodz, central Poland, June 28, 2013. FILE - A Polish Air Force F-16 fighter jet flies near an airbase in Lask near Lodz, central Poland, June 28, 2013.

Another close encounter came Wednesday. Moscow said a NATO fighter jet buzzed Russian Defense Minister Sergei Shoigu's plane as he headed to the Russian military enclave of Kaliningrad, nestled between NATO members Poland and Lithuania. Russian state media reported a Russian SU-27 fighter jet "chased away" the Polish F-16 and published video of the incident.

There's a danger when a plane flies within meters of another, according to defense analyst Pavel Felgenhauer.

"But in the Baltics, that's a kind of pure case of creating tension out of nowhere ... by both sides," he said. "So, it's a bit of a dangerous game. But, in reality, no one wants to fight anyone."

New 'Cold War'

Russian probing of NATO member airspace has increased exponentially since Moscow's 2014 annexation of Ukraine's Crimean Peninsula and ongoing military support for pro-Russia separatists in eastern Ukraine.

"It's no doubt, at least for me, that Russia and the West are in the situation of [a] new Cold War," said defense analyst Alexander Golts, deputy editor of Yezhednevny Zhurnal [Weekly Journal] in Moscow. "[The] Cold War is a situation when you have a problem that cannot be solved ... [not] diplomatically [or] militarily. This problem is Ukraine."

FILE - Russia-backed rebel tanks with a flag of th FILE - Russia-backed rebels' tanks, with a flag of the self-proclaimed Donetsk People's Republic, are seen near Novoazovsk, eastern Ukraine, Oct. 21, 2015. FILE - Russia-backed rebels' tanks, with a flag of the self-proclaimed Donetsk People's Republic, are seen near Novoazovsk, eastern Ukraine, Oct. 21, 2015.

Golts said the issue is that Russia, from its point of view, cannot pull back from its "secret war" in Ukraine, yet until it does so, NATO cannot restore cooperation. Meanwhile, saber-rattling on both sides risks escalation of military conflict.

The United States this week issued new sanctions against Russian entities over their involvement in Ukraine, while the EU agreed to extend its own sanctions against Moscow.

The added sanctions came as Ukrainian President Petro Poroshenko visited President Donald Trump at the White House. Poroshenko later said the U.S. soon would sign some defense deals with Kyiv, but he gave no details. The U.S. so far has provided only training and nonlethal military equipment to Kyiv in an effort to stay out of any direct military conflict with Russia.

Military buildup?

Shoigu said Russia would build up its military forces on its western borders, citing a worsening security situation due to what he called NATO's "anti-Russia course." The Russian defense chief said its military would form 20 new units on its western front this year in response to NATO drills in the Baltic states and Poland.

Soldiers sit atop of amphibious vehicles as NATO t FILE - Soldiers sit atop amphibious vehicles as NATO troops participate in the BALTOPS 2015 sea exercises aimed at reassuring Baltic Sea region allies in the face of a resurgent Russia, in Ustka, Poland, June 17, 2015. FILE - Soldiers sit atop amphibious vehicles as NATO troops participate in the BALTOPS 2015 sea exercises aimed at reassuring Baltic Sea region allies in the face of a resurgent Russia, in Ustka, Poland, June 17, 2015.

The formerly occupied and Soviet states raised concerns about Russian aggression after Moscow's actions in Ukraine. NATO responded with stepped-up deployment of rotational defense forces. Meanwhile, in September, Russia and Belarus are holding large-scale military exercises that simulate a NATO invasion.

The NATO defense alliance deployment is modest compared with Russia's response, said Golts. "And, what is real now — there is no gray zone between these forces. They stand up against each other. And, again, it means any accident can be continued with [a] big war."

Thoughts have turned from potential U.S.-Russia cooperation back to reducing risks of new confrontation, Golts said.

"I think everybody has to forget, for [a] very, very long period of time, the possibility of some kind of cooperation with Russia," he said. "It's more or less clear [that] because of all this scandal with Russian interference in [the] American election, Trump will never approach Mr. Putin," Golts said, referring to Russian President Vladimir Putin.

Syria bluster

Meanwhile, a proxy war in Syria intensifies as Russia and Iran support their ally in Damascus against U.S.-backed Syrian rebels. All sides claim to be fighting Islamic State terrorists.

The U.S.-led coalition in Syria shot down a Syrian warplane this month, as well as two Iranian-made drones that were nearing American-backed troops. Russia condemned the action and said it would treat any plane or drone from the U.S.-led coalition flying west of the Euphrates River as a target.

Moscow also suspended, again, a memorandum aimed at avoiding accidents in the skies over Syria. The first such announced suspension occurred after a U.S. missile strike in April on a Syrian air base that Washington said Damascus used to launch chemical weapons attacks that had killed more than 80 civilians. Russia condemned the U.S. attack and blamed the chemical weapons on Syrian militants.

While many of Russia's implied threats against the U.S.-led coalition in Syria appear to be bluster, the risk of direct conflict between the two sides is increasing, Golts said. "If you just repeat your complaints and your threats, sooner or later, nobody will pay attention. So, it's a problem how to make statements tougher and don't move at the same time closer to [a] condition of war."