US Secretary of State Rex Tillerson used the email alias 'Wayne Tracker' to discuss climate change while he was ExxonMobil's chief executive, according to New York Attorney General Eric Schneiderman.

Mr Tillerson sent messages from the account to discuss the risks posed by climate change, Mr Schneiderman said in a court filing about his office's fraud investigation of the company. Mr Tillerson, whose middle name is Wayne, used the Wayne Tracker account on the Exxon system from at least 2008 through 2015, Mr Schneiderman said.

Mr Schneiderman made the claim in a letter on Monday to Justice Barry Ostrager in New York state court in Manhattan, accusing Exxon of failing to turn over all relevant documents required by a court order. The filing comes in a protracted legal dispute in which Exxon seeks to derail probes by New York and Massachusetts into whether the company misled investors for years about the possible impact of climate change on its business.

Mr Tillerson used the account for "secure and expedited communications between select senior company officials and the former chairman for a broad range of business-related topics," after his primary account began receiving too many messages, Exxon spokesman Alan Jeffers said in an email.