The Energy and Resources Institute (TERI) also said that Vibha Dhawan is the new presiding officer of ICC.
Saikia told PTI that she has resigned but did not give any reason for taking the step.
Replying to an email query, TERI said that Saikia resigned on September 14 and did not given any reasons for her resignation.
"Yes, it is true that I have resigned," Saikia told PTI over phone. "No," she said, when asked whether she had cited any reason for tendering her resignation.
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According to TERI website, Dhawan is responsible for planning and coordination and leading the research for algal biotechnology. She has been with TERI since 1985.
A research analyst at TERI has accused Pachauri of sexual harassment and he is currently on bail in the case. A case of sexual harassment was registered against Pachauri, a Nobel peace prize recipient, on February 13.
TERI governing council had on July 23 appointed Dr Ajay Mathur, currently the director general of Bureau of Energy Efficiency (BEE), as its Director General.
He was recently allowed by a Delhi court to travel to Kazakhstan for a conference on climate change.