Complex sentence: On 17 March 2014, the day after the Crimean status referendum, Surkov became one of the first seven persons who were placed under executive sanctions by President Obam, freezing his assets in the US and banning him from entering the United States.
Split into simpler sentences: On 17 March 2014, the next day after the Crimean status referendum, Surkov became one of the first seven persons who were put by President Obama under executive sanctions. The sanctions freeze his assets in the US and ban him from entering the United States.