"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.
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 defence spending by 11 percent over five year, and the other was to reinforce cooperation with NATO as a whole, as well as with its individual members.
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.