The pictures appeared to show a Pantsir anti-aircraft system installed on the defence ministry building along the Moskva River, which was visible Friday on the main ministry building in the capital.

A video on social media showed a Pantsir system purportedly being hoisted onto the roof of a building in the centre of Moscow.

Another Pantsir system was installed some 10 kilometres (six miles) from President Vladimir Putin's residence in Novo-Ogaryovo outside Moscow, independent Russian-language media reported.

Pantsir-S1 is an air defence system designed to protect against a variety of weapons including aircraft and ballistic and cruise missiles.

Asked whether Russia was concerned that Moscow could be a target, Kremlin spokesman Dmitry Peskov referred questions to the defence ministry.

"They are responsible for ensuring the security of the country in general and the capital in particular, therefore it is better to ask the defence ministry about all measures that are taken," Peskov told reporters.

The ministry did not immediately respond to an AFP request for comment.

Security analyst Michael Horowitz said on Twitter that Russia could be concerned about "Ukrainian attacks against Moscow" or wanted to play up the threat of Ukrainian attacks.

Moscow has accused Ukrainian forces of being behind drone attacks on military infrastructure deep inside Russian territory.

On Friday, Ukraine's Western allies gathered for a major conference to decide on a new package of military aid for the war-torn country.

Putin sent troops to Ukraine in February last year but Moscow's army has suffered a string of military setbacks in Ukraine in recent months.