(BBC) ExxonMobil must pay a $2m penalty for signing documents for oil and gas projects in Russia, despite US sanctions imposed after Russian forces seized Crimea in 2014.
Exxon signed documents in May 2014 with Igor Sechin, the president of Russian oil giant Rosneft and another, unnamed person, it said.
At the time, Exxon was led by Rex Tillerson, now US Secretary of State.
The US Treasury Department said Exxon showed “reckless disregard” for rules.
Exxon has not yet responded to a request for comment.
The US imposed sanctions against Russia amid rising tension in Ukraine. The agreements were announced as Russia annexed Crimea. The US later added Mr Sechin to the list.
Exxon did not disclose the activities, the Treasury Department said. It described it as an “egregious case”.
In its announcement, the Treasury Department said Exxon officials claimed they did not think the sanctions targeted Mr Sechin in his professional role.
Mr Tillerson’s ties to Russia prompted controversy when US President Donald Trump named as his choice to lead the State Department.
As head of the oil company, he signed deals with Rosneft, leading Russia to award him the Order of Friendship in 2013.
The US in April said it would not waive sanctions to allow Exxon to resume drilling in Russia.
The sanctions had exposed Exxon to up to $1bn in losses by the end of 2014, Exxon said.