He added: the "action is fundamentally unfair".
In April 2014, in response to its "continuing provocations in Ukraine", the Obama administration expanded its economic sanctions against Russia, freezing the assets of 17 Russian companies and seven Russians linked to Vladimir Putin, as well as prohibiting US dealings with those parties.
"ExxonMobil demonstrated reckless disregard for USA sanctions requirements", the filing says, calling this "an egregious case" and adding, "ExxonMobil caused significant harm to the Ukraine-related sanctions program objectives".
President Obama signed an executive order establishing sanctions on Russian Federation on March 16, 2014.
The sanctions prohibit USA citizens or those located in the United States from dealing with those on the blacklist, such as Sechin. Tillerson has recused himself from any decisions regarding his former employer for his first two years as Secretary, according to the State Department. He is now responsible for USA foreign policy, which includes helping to make sanctions decisions. State Department spokeswoman Heather Nauert told reporters on Thursday that the agency was alerted to the fine on Wednesday.
Former U.S. Ambassador to Russia Michael McFaul said that while it is a small fine, it is not wholly insignificant.
Exxon did not disclose the activities, the Treasury Department said.
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"Based on the Enforcement Information published today, OFAC is trying to retroactively enforce a new interpretation of an executive order that is inconsistent with the explicit and unambiguous guidance from the White House and Treasury issued before the relevant conduct and still publicly available today".
Exxon plans to challenge the action. The company said the eight legal documents it signed were related to ventures with Rosneft, not Sechin personally. In a statement, the department also noted that the company's "senior-most executives", e.g.
The US Treasury Department said Exxon showed "reckless disregard" for rules.
Because Rosneft itself is not off-limits to Americans, another company executive could have signed the contract with no sanctions risk to ExxonMobil, said David Mortlock, who was a State Department and White House sanctions official during the Obama administration.
The company has long opposed sanctions on Russian Federation.
Tillerson, whom Putin personally awarded Russia's Order of Friendship in 2013, reportedly argued at the time that he was not in favor of sanctions because he believed them to be ineffective, which is definitely the case if you choose to ignore them.
ExxonMobil has since sought permission to operate in Russian Federation.
"The U.S. and European Union sanctions on Russian Federation will remain in place until Moscow reverses the actions that triggered these particular sanctions", Tillerson said earlier this month during a visit to Ukraine.