by 28 august when gnther von kluge in the north had reached the vistula river ( some 10 kilometers from the german border at that time ) and georg von kchler was approaching the narew river , walther von reichenaus armor was already beyond the warta river ; two days later , his left wing was well to the rear of d and his right wing at the town of kielce ; and by 2 september one of his armored corps was on the outskirts of warsaw , having advanced 225 kilometers ( 140 miles ) in the first week of war .