KYIV, March 29 (Reuters) - Ukraine struck a railway depot and knocked out power in the Russian-occupied city of Melitopol deep behind front lines on Wednesday amid growing talk from Kyiv of a counterassault against Russian forces worn out by a failed winter offensive. The average number of daily Russian attacks on the front line reported by Ukraine's general staff has declined for four straight weeks since the start of March, to 69 in the past seven days from 124 in the week of March 1-7. See here for a complete list of exchanges and delays