In a series of early morning tweets over the weekend, President Trump threw a spanner in the months-long efforts of his special envoy to Afghanistan, Zalmay Khalilzad, not only calling off the peace negotiations but also cancelling the hitherto secret, albeit separate, meetings with Afghan President Ashraf Ghani and Taliban No 2, Mullah Abdul Ghani Baradar. Warning terrorist groups of any such misadventure in future, Trump said, "And I'm not even talking about nuclear power".
Mr Trump and First Lady Melania Trump welcomed victims' families and survivors to the White House, where they marked the anniversary with a moment of silence before the president delivered his speech at the Pentagon, where he also laid a wreath.
The number of USA troops peaked at around 100,000 but began to drop steadily after Bin Laden was killed in 2011.
The Taliban regime that had sheltered 9/11-mastermind Osama Bin Laden was ousted by USA -led military forces in 2001 but was never fully routed, maintaining a foothold in Afghanistan for 18 years.
While the United States peace overtures to the Taliban flounder, India has said that the global community should address the problem of sanctuaries for terrorists in Pakistan. I want to talk to these Taliban negotiators.
The latest fighting underscored expectations of an escalation in violence following U.S. President Donald Trump's abrupt cancellation of talks with the Taliban aimed at withdrawing U.S. troops and opening the way to an end to 18 years of war in Afghanistan.
"It looks to me as if this one wasn't quite there", she said.
They set the example, Trump said, for all Americans "today and every day to treasure our liberty, to live up to our values, to prove ourselves worthy to our heroes, to never ever forget". "The support and safe havens enjoyed from beyond Afghanistan's borders by groups such as the Taliban, the Haqqani Network, Daesh [Islamic State], as well as Al Qaeda and its proscribed affiliates, including the Lashkar-e-Taiba and Jaish-e-Mohammed, must be addressed", he said. "Over the last four days, we (US troops) have hit our enemy harder than they have ever been hit before".
What's the likely effect of the decision on the 14,000 American troops still in Afghanistan?