The 79-year-old Jha died due to various problems including organ failure, cardiac arrest and septic shock in the national capital.
Jha was Union minister of State for Heavy Industries and Public Enterprise in the UPA government led by former Prime Minister Manmohan Sing.
In his condolence message, Kumar said Jha "was a skilled political leader and a devoted social worker" and prayed that his family members find the strength to bear the loss.
Deputy Chief Minister Sushil Kumar Modi also mourned the death of Jha, who was a minister of state in the previous Manmohan Singh government at the Centre.
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"Bihar's polity has suffered an irreparable loss by the death of Shri Raghunath Jha", the Dy CM said in his condolence message.
Leader of the opposition in the state assembly Tejashwi Yadav said in a tweet "shocked over the demise of Jha who was a guardian, family friend and a top RJD leader.....it is a personal loss".
A close confidant of Yadav's father and RJD supremo Lalu Prasad, Jha remained with the party for most part of his political career notwithstanding occasional spats which saw him switching over, for brief periods, to the Samata Party and the Samajwadi Party.
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