Russian intelligence has warned of an increased risk of Taliban or Islamic State fighters invading Central Asia, the Associated Press reports.

FSB director Alexander Bortnikov said in comments carried by Russian news agencies on Wednesday, October 28, that a concentration of Taliban fighters, some of whom had pledged allegiance to the Islamic State group, at Afghanistan's northern border make the risk of invasion tangible.

Afghanistan shares a porous border with the former Soviet republics of Turkmenistan, Uzbekistan and Tajikistan, which has been a source of drugs coming into Russia and is a longstanding worry of Moscow's.

Putin earlier this month called the situation in Afghanistan "close to critical" and called on other ex-Soviet nations to be prepared to act together to repel a possible attack.