Watch: President Donald Trump Speaks at Pentagon on 9/11 Anniversary

President Donald Trump spoke at the Pentagon in Arlington, Virginia on the 18th anniversary of the 9/11 terrorist attacks after laying a wreath at the Pentagon Memorial and standing for a moment of silence for the 184 victims.

"For every American who lived through that day, the Sept 11 attack is seared into our soul," the president said as he remembered the day.

He recalled his personal memory of the day, saying that he was sitting at home watching a "major business television show" when "all of the sudden" the screen cut away. "Nobody really knew what happened, there was great confusion," Trump said.

The president said he watched as the second plane at "tremendous speed" crashed into the second World Trade Center Tower.

"It was then I realized the world was going to change," he said.

The president also remembered some Pentagon victims by name, thanking their surviving family members who were at the event.

"To each of you, the first lady and I are united with you in grief," he said. "We come here in the knowledge that we cannot erase the pain or reverse the evil of that dark and wretched day. But we offer you all that we have: our unwavering loyalty, our undying devotion and our eternal pledge that your loved ones will never, ever be forgotten."

During his speech, he mentioned his canceled plans with the Taliban, which were scheduled to take place at Camp David close to the anniversary of the 2001 attacks. "I called them off when I learned that they had killed a great American soldier from Puerto Rico," he said.

"They thought they would use this attack to show strength but actually what they showed is unrelenting weakness," he said, referencing the the Taliban car bomb that killed a US soldier and 11 others last week.

Trump claimed that in the last four days, "We have hit our enemy harder than they have ever been hurt before and that will continue."

And, he warned, "If for any reason they come back to our country, we will go wherever they are and use power the likes of which the United States has never seen before." He clarified that the US would not use nuclear power but said "They have never seen anything like what will happen to them."

Earlier in the morning at Ground Zero in New York City, friends and family of those who died in the attacks at the Twin Towers read the names of the victims in between moments of silence at the times that the two planes crashed into the North and South Towers.