Russia's military maneuvering continued Monday over the waters of the Baltic Sea, where a Russian fighter jet was intercepted by NATO aircraft. The Latvian army reported via Twitter that NATO F-16 fighter jets intercepted a Russian Su-27 fighter Monday, just a day after the Northern European nation's army stated on the social media site that it had spotted three Russian navy vessels including a Kilo-class submarine in international waters off its coast.

In September NATO promised to help Latvia, Estonia and Lithuania maintain their security, as the situation in Ukraine continued to simmer and Russia loomed as a potential threat to the former Eastern Bloc nations. Sightings of Russian military aircraft and navy ships have been happening with increasing frequency over recent weeks, raising concerns about President Vladimir Putin's military and strategic intentions.

The military movements are "not normal," Tom Nichols, a professor at the U.S. Naval War College and senior associate at the Carnegie Council on Ethics and International Affairs, told Business Insider. "[I]t clearly comes from the very top as an expression of Putin’s foreign policy.”

Putin told German TV network ARD Sunday that Russian air and naval movements are taking place “exclusively in the international waters and over international airspace,” according to Bloomberg.

NATO identified Russian military planes over the Atlantic Ocean and the Baltic and North Seas last month, and Russia's minister of defense said last week the country would send aircraft to patrol in the Gulf of Mexico. A group of Russian navy warships also appeared near Australia during the recent G-20 summit in a move seen as a direct provocation of Australian Prime Minister Tony Abbott.

"Certainly it is unusual for Russian naval elements to be in Australian waters,” Abbott said. "Unusual, not entirely unprecedented, but unusual ... Let’s not forget that Russia has been much more militarily assertive in recent times.”

Meanwhile, Maxim Raku, a spokesman for the Russian embassy in Canberra, told Fairfax Media that the ships' movement was “not directly related to Australia,” the Telegraph reported.

"Your reaction is not that surprising because we do rarely go this way," Raku said. "We really don't break any rules, we stick to international law, so why should we be seen as a danger?"