President Donald Trump on Wednesday said the United States has hit the Taliban “harder than they have ever been hit before” just days after he canceled a secret Camp David meeting with Taliban leaders and declared the peace talks dead.

Trump’s comments came as he spoke at a remembrance ceremony for the 18th anniversary of the September 11 attacks.

“And 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 used before – and I’m not even talking about nuclear power. They will never have seen anything like what will happen to them,” Trump said.

Trump scrapped talks with the Taliban planned for Camp David, Maryland, over the weekend after an American soldier was killed by a suicide bomber in the capital Kabul last week.

Trump had hoped to cap months of US negotiations with the Taliban militants, who control large parts of Afghanistan, with a secret meeting at Camp David that would include Afghan President Ashraf Ghani and was aimed at securing an agreement to pull US troops out of America’s longest war of 18 years.