Russia on Friday condemned NATO's invitation to Montenegro to become its 29th member, saying the step risked fuelling tensions in Europe. NATO's move Thursday angered Russia, which feels threatened by a NATO expansion right up to its borders.

"In general, our stance is that NATO's further expansion is a negative process," Kremlin spokesman Dmitry Peskov told reporters, according to Reuters. "This process yields nothing from the point of view of European security."

Peskov also reportedly said: "On the contrary, this process risks further increasing tensions on the continent."

Before Montenegro joins NATO, legislative bodies of all 28 nations, including the U.S. Senate, must issue its approval.

"Montenegro has already been contributing to NATO, EU and UN operations, promoting regional cooperation in the Balkans, and implementing major reforms," NATO Secretary General Jens Stoltenberg reportedly said Thursday. "Membership will give Montenegro the ability to help shape NATO policy. It will bring more stability and security to the region ... and it will be a clear sign that NATO's door remains open to partners that share and promote our values."

However, Russia threatened to "change its policy ... to this friendly country" if Montenegro became a new member.

A Russian foreign ministry spokeswoman called the potential NATO expansion another "attempt to change the military political landscape in Europe, especially in the light of the alliance's course to restrain our country."

Since Russia annexed Ukraine's Crimean Peninsula in 2014, NATO has increased its military presence across Europe, including in the Russian populated Baltics.