Even as the hunt is on for a new chairman following the ouster of Cyrus Mistry, Tata Sons on Friday announced major changes in their organisational structure, including the resignation of three top executives.

"Nirmalya Kumar, N.S. Rajan and Madhu Kannan have decided to explore options outside Tata Sons and have left the services of the company," a statement from the group said.

The trio was seen to be close to Mistry.

The group said human resources will be overseen by S Padmanabhan in addition to his existing responsibilities of leading the Tata Business Excellence Group, while Mukund Rajan will continue to be responsible for ethics and sustainability.

Rajan is also being given the additional responsibility of overseeing the operations of the overseas representative offices of Tata Sons in the US, Singapore, Dubai and China.

This apart, Harish Bhat, who oversees marketing and customer affairs, will also be responsible for managing the Tata Brand. "In the interim, he will also oversee the functions of Strategy and Business Development," the statement said.

Among the others, Gopichand Katragadda continues as Group Chief Technology Officer, and Sanjay Singh as Chief of Public Affairs out of the Delhi office.