Taliban insurgents have made advances in the Afghan province of Kunduz, bordering Tajikistan, while the prospect of Islamic State-trained militants arriving in the region from the conflict in Syria have increased security fears among Russia and its Central Asian allies.

Speaking after meeting Russian President Vladimir Putin on Thursday, Kazakh President Nursultan Nazarbayev said they were "very concerned with the situation in Tajikistan".

Russian military used to patrol Tajikistan's sensitive border with Afghanistan, pulling out in 2005 by agreement with the local government.

Asked by Reuters if Moscow might re-establish its control of Tajikistan's border with Afghanistan, Russian Deputy Defence Minister Yuri Borisov said: "I don't rule it out."