Charges that Exxon Mobil misled the public about the potential industry impacts on the environment are tainted by political motivations, the company said.

The attorney generals from 20 states announced plans to work with environmental campaign groups on ongoing or potential investigations into whether Exxon misled investors decades ago about the impact their business had on climate change. The New York Attorney General's office issued a subpoena to Exxon last year following a series of reports saying the company was misleading investors.

Carroll Muffett, president of the center for International Environmental Law, said the combined interest in pressuring Exxon highlights the gravity of the situation.

"A critical mass of states now considers the evidence against Exxon sufficiently serious to justify exploratory cooperation on climate related investigations and to justify the use of words like 'misinformation', 'deception' and, most significantly, 'fraud,'" he said in a statement.

In defending itself against the New York attorney general, Exxon said the allegations were inaccurate, deliberately misleading and charged "activists" with exploiting the issue. The company said its research widely mirrored the global understanding of climate issues at the time.

Suzanne McCarron, a spokesperson for the company, said in a written statement the company was actively examining all of its legal options in response to the latest allegations from the state attorneys general. Most of the pressure, she added, is politically motivated and based on reports funded by those organizations working against the fossil fuels industry.

"The allegations are based on the false premise that Exxon Mobil reached definitive conclusions about anthropogenic climate change before the world's experts and before the science itself had matured, and then withheld it from the broader scientific community," she said. "Such a claim is preposterous."

Exxon is facing mounting pressure from investors wary of betting on the industry. Last week, the Rockefeller Family Fund, the philanthropic arm of the family whose fortune was founded on oil, said it was dismantling its investments in the industry. The family said the "morally reprehensible conduct" of Exxon was in part behind a decision to divest from fossil fuels.