Trump presides over his 1st 9/11 ceremony for '2,977 innocent souls' as president Trump commemorates 9/11 at the Pentagon.

 -- President Donald Trump and first lady Melania Trump attended a commemoration ceremony this morning at the National 9/11 Pentagon Memorial, marking the 16th anniversary of the Sept. 11 terrorist attacks.

"For the families with us on this anniversary, we know that not a single day goes by when you don't think about the loved ones stolen from your life," Trump said at the ceremony. "Today, our entire nation grieves with you and with every family of those 2,977 innocent souls who were murdered by terrorists 16 years ago."

"On that day not only did the world change, but we all changed," Trump said. "Our eyes were opened to the depths of the evil we faced, but in that hour of darkness we also came together with renewed purpose. Our differences never looked so small, our common bonds never felt so strong."

Secretary of Defense James Mattis and Chairman of the Joint Chiefs of Staff Gen. Joseph Dunford hosted the ceremony honoring the 184 people killed in the attack at the Pentagon.

The president also laid a wreath at the 9/11 memorial at the Pentagon.

Trump offered the nation's prayers to the states in the path of Hurricane Irma and recovering from Hurricane Harvey.

At 9:37 a.m. today, the exact time when American Airlines Flight 77, carrying 64 people on a flight bound for Los Angeles, was flown into the side of the Pentagon on Sept. 11, 2011, the president led a moment of silence on the South Lawn of the White House.

It’s the first time Trump has led a Sept. 11 commemoration ceremony as commander in chief.

Meanwhile, the president was to receive “a comprehensive picture of the terrorist threat environment and what we're doing to counter it from his senior officials on 9/11,” Homeland Security adviser Tom Bossert told reporters at the White House on Friday.

“No terrorist should view us as vulnerable right now, farthest thing from the truth,” Bossert said. “Second, there is no actionable, credible threat to the United States right now.”

Bossert said Trump intends to continue the practice of receiving a briefing about the terrorist environment on Sept. 11, a custom started by President George W. Bush and continued under President Barack Obama.

Vice President Mike Pence is in Shanksville, Pennsylvania, for a separate ceremony at the location of the Flight 93 Memorial.

Last week, Trump proclaimed Sept. 11 as “Patriot Day.”

“We rededicate ourselves to the ideals that define our country and unite us as one,” said Trump in a statement, “as we commemorate all the heroes who lost their lives saving others.”

ABC News’ Alexander Mallin contributed to this report.