By Tom Balmforth, Max Hunder and Jonathan Landay KYIV/FRONTLINE NORTH OF KHERSON, Ukraine (Reuters) -Ukrainian troops pushed towards the southern strategic river port of Kherson after Moscow ordered one of the war’s biggest retreats, although officials fear Russian troops could still turn Kherson into a “city of death” as they expect it will take at least a week to withdraw. Ukraine’s Defence Minister Oleksii Reznikov told Reuters in an interview on Thursday that Russia had a contingent of 40,000 troops in Kherson region and intelligence showed its forces remained inside the city, around the c…