Russia’s “aggressive posturing” in Europe has led leaders from nine central and eastern European states to issue a joint statement Wednesday, Reuters reported. The leaders backed a strong NATO presence in the region, an alliance Moscow has long viewed as encroaching on its sphere of influence.

“We will stand firm on the need for Russia to return to respect of international law as well as of its international obligations, responsibilities and commitments as a precondition for a NATO–Russia relationship based on trust and confidence,” the joint statement said.

Polish President Andrzej Duda said NATO faces threats from both the east and the south, necessitating “more troops, more infrastructure and more common actions.” The military and political alliance is currently undertaking its largest military exercises in more than a decade.

Lithuania, Latvia, Estonia, Slovakia, Bulgaria, Hungary, Romania, Poland and the Czech Republic were the nine countries that signed the statement. Fears over Russia’s recent actions began with the March 2014 annexation of the Crimean peninsula from Ukraine. After the annexation, a conflict broke out in eastern Ukraine, pitting Ukrainian government forces against Russian-backed separatists. The war has left more than 8,000 dead and displaced more than 1.4 million.

The statement said leaders would work together to ensure deeper cooperation with NATO and the European Union. Hybrid warfare, cyber defense, energy security and strategic communication were listed as key areas for the nations to concentrate on.

Several nations have announced plans to boost their military and defense spending. Poland is in the midst of modernizing its armed forces, and the Czech Republic has also announced it intends to purchase more weapons for its military. Nordic states also reported Russian aggression along their borders and in the Arctic, with Norway saying it needs to modernize its defense forces.

The statement from the nine countries comes on the same day Russia celebrates National Unity Day. Russia began airstrikes over Syria Sept. 30, prompting concerns over the Kremlin’s increasing range of military involvement from Europe to the Middle East.