MASCOW - Russian President Vladimir Putin on Friday warned that violence in Afghanistan could spill over into ex-Soviet Central Asia, a day after the US announced it would keep thousands of troops in the conflict-wracked country.

"The situation there (in Afghanistan) is genuinely close to critical," Putin said at a meeting of leaders from the ex-Soviet region in Kazakhstan.

"Terrorists of different stripes are gaining more influence and do not hide their plans for further expansion," Putin told the summit of the Commonwealth of Independent States (CIS).

"One of their aims is to break into the Central Asian region. It is important for us to be ready to react in concert to this scenario," Putin said in a speech posted on the Kremlin's website.

US President Barack Obama on Thursday said American troops would remain in Afghanistan past 2016, retreating from a major campaign pledge as he admitted Afghan forces were not ready to stand alone against the resurgent Taliban.

Russia has military bases in the ex-Soviet nations of Kyrgyzstan and Tajikistan and - with local militaries ill-equipped - many in the region look to Moscow to shore up the region's vulnerable southern frontier with Afghanistan. (AFP)