Russia is losing 5 of its soldiers for every Ukrainian it kills in the war's bloodiest battle, NATO official tells CNN

• Russia has lost at least five soldiers for every Ukrainian soldier killed in Bakhmut.
• This is according to an informed estimate by a NATO official who spoke to CNN.
• Ukraine has also suffered significant losses while defending the ruined city, the official said.

The Russian effort to take Bakhmut, a former salt-mining city in eastern Ukraine, has become one of the longest and bloodiest battles in the war. And NATO intelligence estimates suggest it has been especially bloody for the Russian side.