Excellent photo. Hopefully you were not standing too close to it.

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Perhaps the Vipera kaznakovi - Viper Caucasas.

At first didn't think so, but found a couple of photos which seemed to fit.

https://en.wikipedia.org/wiki/Vipera_kaznakovi

http://knowledgebase.lookseek.com/Caucasus-Viper-Vipera-kaznakovi.html

http://www.stlzoo.org/animals/abouttheanimals/reptiles/snakes/caucasusviper/

Looking at these probably not the Vipera Kaznakovi :
https://www.google.com.au/search?q=Viper...ZEEBKwQ_AUIBygB

Common Viper

http://www.sibserpent.com/products/snakevenoms/viperaberus.html

Gloydius

https://en.wikipedia.org/wiki/Gloydius

East of the Urals so probably not.

Saw-scaled viper

https://en.wikipedia.org/wiki/Echis

No I do not think so.

Probably a melantistic (black) common adder. The head shape is right.

http://homepage.ntlworld.com/highexplosi...dder/Adder.html

Or Grass snake

http://alexisphoenix.org/romaniasnake.php

Head shape is right for a grass snake. Grass snake is not venomous. Common viper is.