WASHINGTON — The Trump administration for the first time on Monday formally blamed Iran for the presumed death of retired FBI agent Robert Levinson, publicly identifying two Iranian intelligence officers believed responsible for his abduction and imposing sanctions against them.

Levinson disappeared in Iran under mysterious circumstances more than a decade ago, and though U.S. diplomats and investigators have long said they thought he was taken by Iranian government agents, Monday’s announcement in the final weeks of the Trump administration was the most definitive assignment of blame to date.

Besides calling out two high-ranking intelligence officers by name, U.S. officials also said the Iranian regime sanctioned the plot that led to Levinson’s abduction and lied for years about its involvement in his disappearance through disinformation campaigns aimed at deflecting responsibility and covering up the government’s role.

“The abduction of Mr. Levinson in Iran is an outrageous example of the Iranian regime’s willingness to commit unjust acts,” Treasury Secretary Steven Mnuchin said in a statement. “The United States will always prioritize the safety and security of the American people and will continue to aggressively pursue those who played a role in Mr. Levinson’s detention and probable death.”

The Iranian intelligence officers, Mohammad Baseri and Ahmad Khazai, are alleged to have been involved in Levinson’s abduction and probable death. Under the sanctions, any property or assets they hold in the United States would be frozen. Though it’s unlikely they have bank accounts in the U.S., the sanctions could also limit their movements or financial dealing outside Iran. The men have met with intelligence officials from other countries and also led delegations, U.S. officials say.

There was no immediate reaction in Iranian state media Monday night to the announcement.

In a statement, the Levinson family thanked Trump administration officials and called Monday’s announcement “just one step in a long road toward achieving justice for him, but it is an important one.”

“Robert Levinson will never come home to his family alive because of the cruel, cynical and inhumane actions of the Iranian authorities,” the family said. “Because of these men and others like them, our wonderful husband, father and grandfather died alone, thousands of miles from everyone he loved.”

Monday’s announcement is the latest in a series of increasingly aggressive Trump administration actions against Iran since the president two years ago withdrew from the landmark 2015 Iran nuclear deal, a signature foreign policy achievement of predecessor Barack Obama.

In the last few years, the Trump administration has steadily ramped up pressure on Iran, reimposing a wide swath of sanctions and taking other actions, including killing the head of the Islamic Revolutionary Guards Corps in a drone strike at the airport in Baghdad this year.

That move, coupled with retaliatory attacks against Iranian-backed militias in Iraq, stepped-up sanctions against Iranian proxies in Lebanon and Yemen and the recent killing of an Iranian nuclear scientist outside of Tehran that has been attributed to Israel, have left the impression that Trump is seeking to box in President-elect Joe Biden when he takes office in January.

Biden has said he wants to reenter the 2015 nuclear deal but also improve and expand on it. Those prospects may prove difficult to realize if the situation escalates in the next five weeks.