Donald Trump has been branded insensitive after greeting supporters with a double fist-pump ahead of a 9/11 memorial. 

The US President’s less-than-sombre reaction was captured on Tuesday as he arrived in Pennsylvania, along with First Lady Melania Trump, on his way to pay respects to the fallen heroes of United Airlines Flight 93.

The plane crashed as passengers and flight crew thwarted the hijacking by a group of terrorists 17 years ago. 

Footage of Trump’s jubilant reaction to onlookers was instantly shared by reporters and widely condemned on social media. 

Nearly 3,000 people died on 11 September 2001, when other planes were flown into New York’s World Trade Center and the Pentagon in an attack planned by al-Qaida leader Osama bin Laden.

Bin Laden was killed almost a decade later, in May 2011, during a military operation ordered by President Barack Obama.

In a statement ahead of Trump’s Tuesday speech, White House press secretary Sarah Huckabee Sanders said the president’s focus for the day was “remembering the lives that were lost, and certainly honouring the individuals who were not only lost that day, but also put their lives on the line to help in that process”.

While on his way to the memorial service, the president tweeted: “17 years since September 11th!”.

He also posted praise for his private counsel Rudy Giulani who he said did a “great job” as mayor of New York City during the attacks 17 years ago.

Trump observed the anniversary for the first time as president last year, along with the first lady, at the White House.