March 6 (Reuters) - Russian mercenary boss Yevgeny Prigozhin said his representative had been denied access to the headquarters of Russia's military command in Ukraine on Monday, in a further deepening of his rift with the defence establishment. Prigozhin's private militia, Wagner, has led much of the heaviest fighting for the Ukrainian city of Bakhmut, but he has complained bitterly for weeks that the military leadership is belittling its contribution. See here for a complete list of exchanges and delays