"The electoral reverses in the latest round of by-polls call for a deep introspection by BJP leadership to find out reasons behind defeat," he told reporters here.
It is a 'matter of concern' that BJP has faced electoral setback in key states like Uttar Pradesh and Rajasthan soon after the impressive mandate in the general elections, Thakur, who was health minister in the Atal Bihari Vajpayee government, said.
Thakur rued the marginalisation of a number of veteran leaders within the party and said a barrier has been created to deprive charge to those attaining 75 years of age or beyond to work in government and decision-making process within the party.
"The BJP leadership should remove the artificial barrier and give an opportunity to eligible MPs irrespective of their age to work with government," he said.
Thakur, a former state unit BJP chief, has been known as an ardent Modi supporter could not be given any ministerial berth because of his age.