President Pranab Mukherjee Wednesday congratulated the Defence Research and Development Organisation (DRDO) for successfully test-firing the Agni-IV strategic missile."I extend my heartiest congratulations to all those associated with the successful test-firing of Agni-IV strategic missile," the president said."I hope this achievement will inspire our scientists and all armed forces and defence personnel to make even greater efforts to boost India's indigenous defence capabilities in technologically challenging areas," he said in his message to Avinash Chander, scientific advisor to the defence minister and secretary at the department of defence research and development.The 4,000 km-range Agni IV, an intermediate ballistic missile capable of carrying a one tonne nuclear warhead, was successfully test-fired Tuesday from a launch pad in Wheeler Island, a defence base in Odisha.The DRDO works under the department of defence research and development of the defence ministry.