SAN FRANCISCO, Sept. 18 (Xinhua) -- U.S. electric vehicle manufacturer Tesla said Tuesday it has been contacted by the Department of Justice (DOJ) over its Chief Executive Officer Elon Musk's tweets last month about taking Tesla private.

"Tesla received a voluntary request for documents from the DOJ and has been cooperative in responding to it," Tesla said in a statement.

But the listed company said it has not "received a subpoena, a request for testimony or any other formal process," and promised to completely cooperate with federal regulators over the matter.

It said the request followed "Elon's announcement that he was considering taking the company private" last month, when he tweeted that funding had already been secured for a proposed privatization.

"We respect the DOJ's desire to get information about this and believe that the matter should be quickly resolved as they review the information they have received," Tesla said.

An earlier report said that the DOJ will open a criminal investigation into Musk's statement along with an inquiry by the Securities and Exchange Commission (SEC) about whether it was legal or not for Musk to tweet about the privatization plan.

Musk's move to tweet about a possible privatization plan and secured funding runs the risk of civil and criminal penalties for harming the interests of investors if it is found that he had not secured financing for the privatization deal at the time of the privatization tweets.

Musk backed off from his privatization tweets later in August after they surprised investors and caused an uproar. He later acknowledged that it was in the interest of all people to keep Tesla public.