India has approved a $2.4-billion proposal from French defence groups to upgrade its fleet of 51 ageing Mirage fighter jets, a military source said on Thursday. \"The defence secretary has agreed to the proposal put forward by French defence majors Dassault and Thales and (European group) MBDA for the Mirage-2000 retrofit,\" the source in the Indian Air Force (IAF) told AFP. The upgrade is expected to include advanced navigation systems, mission computers, electronic warfare systems and radars. The work is likely to take nine years and will see two of the Mirages being retro-fitted in France. The remaining aircraft will be upgraded at the state-owned Hindustan Aeronautics base in Bangalore. The deal had been stuck for five years due to differences over costs and the proposed benefits to the IAF, the Press Trust of India news agency said. Overhaul of the fleet will add 20-25 years to the life of the Mirages, which joined the Indian air force in the mid-1980s.