President Obama announced Wednesday that the American government had confirmed the execution of reporter Steven Sotloff by the Islamic State of Iraq and Syria, calling the second beheading of a U.S. journalist in recent weeks “a horrific act of violence.”

“Steven’s life stood in stark contrast to those who murdered him so brutally,” Obama said during a press conference in Estonia on the eve of a NATO summit in Wales.

“Whatever these murderers think they'll achieve by killing innocent Americans like Steven, they have already failed," the president added.

ISIS released the Sotloff video after killing U.S. journalist James Foley in a similar fashion. The executions have placed greater pressure on Obama to confront ISIS more forcefully.