NATO member Poland on Monday signed a deal on military cooperation with non-member Sweden amid concerns raised by increased Russian military activity in the Baltic, according to AFP.
"Once a sea of peace, the Baltic has become a sea of danger," Polish Defence Minister Tomasz Siemoniak told reporters at a joint press conference in Warsaw with Swedish counterpart Peter Hultqvist, AFP reported.
Hultqvist said the increased presence of Russian warships and warplanes in the Baltic Sea had prompted Stockholm to take "two strategic decisions."
One was to boost defense spending by 11% over five years, and the other was to reinforce cooperation with NATO as a whole, as well as with its individual members.
Sweden's foreign ministry on Friday summoned Russia's ambassador after Moscow threatened "retaliatory measures" if the Scandinavian country joined NATO.
The increased tensions come on the heels of Russia's 2014 annexation of Ukraine's Crimean peninsula and backing of separatist forces in the country's east.