We have no way of knowing just how small of a nuke any country that has nuclear weapons has developed. My best guess is that they have developed much smaller bombs than the vast majority consider doable. I mentioned the Soviet Union's Tsar Bomba for a reason. It was so big it was useless as a weapon. It took their biggest transport plane highly modified with the bombay doors removed as well as a system of booster rocket engines just to get it off the ground. Then the big lumbering plane released the bomb using parachutes to pull it out of the plane. The plane and it's companion plane with all of the data collection and filming equipment had to bank and hammer the throttles just to get away from the bomb before it went off. They had attatched massive parachutes to slow its descent. Even then the plane that dropped it instantly dropped a kilometer when the shock wave hit it.
My point to all of this is that this was an early nuke designed not as a weapon in the normal sense but as a weapon of terror.
Fast forward to perhaps the 80s when Russia's so called suitcase bombs were built. That's quite a reduction in size and yeald. Can we honestly think no progress has been made in the last 3 or 4 decades in making even smaller weapons for pinpoint bombing....even small enough to destroy just a few blocks of a city or even smaller yet?
I think it is pretty much accepted that the US and others have technology that is decades beyond what we are aware of.
Look, I'm not trying to prove something I know nothing about, but I do suspect Russia may be using something other than conventional weaponry against terror groups.