Russia is working on setting up a joint air defence system with all of its ex-Soviet military allies, a senior official said Wednesday.

"The merger of regional air defence systems will pave the way for creating a common air defence (system) over the entire territory of the Collective Security Treaty Organisation," Nikolai Bordyuzha, the head of the Russia-led alliance of six countries, told a press conference in the Armenian capital Yerevan.

CSTO, Russia's answer to NATO, groups Russia, Armenia, Belarus, Kazakhstan, Kyrgyzstan, and Tajikistan.

Moscow has a joint air defence system in place with Belarus and Kazakhstan, and the agreement to create one with Armenia "is being considered for ratification" by the two countries' parliaments, Bordyuzha said.

Moscow has stepped up military cooperation with its CSTO allies since becoming embroiled in its worst standoff with the West since the Cold War over its 2014 annexation of the Crimea peninsula from Ukraine and the subsequent start of a pro-Russian uprising in Ukraine's east.

Russia, for its part, accuses NATO of expanding its military reach close to its borders.

In May, Russian President Vladimir Putin warned Washington that Moscow will consider measures to "end threats" from NATO's anti-missile systems in Europe that are based essentially on US technology.

The Western military bloc's missile shield includes the progressive deployment of missile interceptors and powerful radar in eastern Europe and Turkey.

NATO and the United States said this spring that they will switch their defence doctrine from assurance to deterrence in eastern Europe in response to a "resurgent and aggressive Russia".