The BACKFIRE is a long-range aircraft capable of performing nuclear strike, conventional attack, antiship, and reconnaissance missions. Its low-level penetration features make it a much more survivable system than its predecessors. Carrying either bombs or AS-4/KITCHEN air-to-surface missiles, it is a versatile strike aircraft, believed to be intended for theater attack in Europe and Asia but also potentially capable of intercontinental missions against the United States. The BACKFIRE can be equipped with probes to permit inflight refueling, which would further increase its range and flexibility.
After designing the TU-22, the Tupolev design bureau started working on a new bomber that was based on the TU-22. Initially Tupolev considered modifying the TU-22 by changing the angle of the swept wings and equipping it with more powerful engines. However after developing the design "106" and various analysis, the design did not meet the flight characteristic requirements. Tupolev also developed the design "125". The aircraft was supposed have two VK-6 engines, a range of 4500-4800 km and an operating speed of up to 2500 km/h. The design provided for the use of titanium alloys and advanced electronic systems.
Source : www.fas.org