Their first-ever military pact turns Central Asia's largest countries into strategic partners, say observers.
Militants who regard Afghanistan and Pakistan as 'Khorasan Province' in their idea of a caliphate could move the theatre of war from the Middle East to Central Asia, observers warn.
Russia provides weapons and financial support to the Taliban, undermining the Afghan government's counter-terrorism efforts, say officials.
Uzbekistan ranked second in a worldwide survey of respondents' sense of security, but police are taking no chances.
Kazakhstani soldiers are gaining 'invaluable experience' during Exercise Steppe Eagle, say observers.
The drill is meant to strengthen security in Tajikistan and its neighbours as well as to boost regional co-operation, say organisers.
The exchange of ideas and experiences during the exercise helps build trust, build up security and stability in Central Asia, observers say.
Tajik and foreign troops are learning from each other in Exercise Regional Co-operation 2017.
Five state agencies work together to block illegal content online as well as seize printed materials with radical views.
EU intends to strengthen co-operation with Central Asian states to fight terrorism and increase border security, EU representatives to Kyrgyzstan say.