NATO's parliamentary assembly on Monday called on members of the Western military alliance to be ready to respond to the "potential threat" of Russian aggression against them.

The assembly issued a unanimous declaration of proposals after a three-day meeting in Tirana, ahead of a landmark NATO summit in Warsaw in July.

"The challenge from Russia is real and serious," said Michael Turner, the US president of the assembly, which gathered around 250 lawmakers from the 28 member states.

The declaration expressed regret over "Russia's use of force against its neighbours and attempted intimidation of (NATO) Allies".

It said this had "left NATO no choice but to consider the prospect of aggressive Russian action against an Alliance member as a potential threat, and to adopt measured, proportionate responses".

The assembly's declaration also urged NATO allies to "provide reassurance" to members who feel their security is under threat, especially on NATO's eastern and southern flanks.

At the Warsaw summit, NATO leaders will formally endorse an alliance revamp putting more troops into eastern European member states as part of a "deter and dialogue" strategy.

Russia fiercly opposes the move, meant to reassure eastern allies spooked by its 2014 annexation of the Crimean peninsula from Ukraine and the pro-Moscow revolt that followed in the country's east.

NATO Secretary General Jens Stoltenberg echoed the parliamentary assembly's stance during a Monday visit to alliance member Poland.

Speaking in Warsaw, he said NATO was sending a "clear signal to any potential adversary that an attack on Poland will be considered an attack on the whole alliance."

Along with Romania, Poland became a target for Russian ire after it agreed to host a US and NATO anti-missile system that Moscow regards as a security threat.

NATO, however, insists the shield is not directed against Russia, but is instead designed to counter threats from so-called "rogue states" in the Middle East.

"It is directed against threats coming from outside the Euro-Atlantic area," Stoltenberg insisted.

NATO cut all practical cooperation with Moscow following Russia's Ukraine intervention, but the US-led alliance has said it will hold formal talks with Moscow before the July 8-9 summit.

In April, the NATO Russia Council (NRC) held its first meeting since June 2014 but the talks ended in "profound disagreements" over Ukraine and other issues, although Stoltenberg said at the time it was a useful exchange.

The assembly said NATO should explore ways to "reduce tensions" with Moscow, while "addressing Russia's unacceptable violations of international norms".

It also called on NATO to strengthen conventional and nuclear deterrence, and to increase cooperation with European Union border agency Frontex over the migration crisis.