Russian President Vladimir Putin said that while Moscow does not consider Finland and Sweden's decision to join NATO as a threat, deployment of military infrastructure there may trigger a response.

The expansion of NATO to Sweden and Finland poses "no direct threat for us ... but the expansion of military infrastructure to these territories will certainly provoke our response," Putin said during a televised summit meeting of the Collective Security Treaty Organisation (CSTO), a Moscow-led military alliance.

Enlargement of NATO to include Sweden and Finland would be a serious blow to Putin, who sees the alliance’s post-Cold War expansion in Eastern Europe as a threat. Putin has cited it among his reasons for attacking Ukraine. His spokesperson, Dmitry Peskov, said Monday that Russia "will look carefully at what the consequences will be of Finland and Sweden joining NATO."

NATO's Secretary General Jens Stoltenberg has said the membership process for both Finland and Sweden could be very quick – though member Turkey has cast some doubt over the move as the two Nordic countries refuse to stop supporting terrorist groups and extradite terrorist suspects.

Swedish Prime Minister Magdalena Andersson said Monday that joining the 30-member military alliance was her country's best defense in the face of Russian behavior.

"Unfortunately, we have no reason to believe that the trend (of Russia’s actions) will reverse in the foreseeable future," she said.