Today marks 20 years since the world stood still and watched on in horror as the 9/11 terrorist attacks played out on TV screens around the world.

Nineteen men hijacked four commercial aeroplanes on the morning of September 11, 2001, and travelled towards major US landmarks in an attack orchestrated by al Qaeda leader Osama bin Laden.

A total of 2,977 people were killed as a result of the attacks, which also triggered the 20-year war in Afghanistan.

As we remember those who lost their lives, MPs have taken to twitter today to pay their respects to the victims.

Watford MP Dean Russell said: “20 years on from the awful events of 9/11, we remember all of those who died as a result of those terrible attacks, their families, and all of those that survived but remain affected by the events of that day.”

Hertsmere MP and Culture Secretary Oliver Dowden added: “Today, we remember the 2,977 who lost their lives in a tragic attack that shook the world 20 years ago.

“My thoughts are with their loved ones, and all those who were affected by this horrific incident. The victims will never be forgotten.”

St Albans MP Daisy Cooper said: “Twenty years on, we remember the horrific scenes from a shocking attack that shook the world.

“An attack on our liberties, freedoms, democracy, and more. Today, we remember all those who lost their lives and all those who lost loved ones, friends, and family members.”

Hertfordshire Fire and Rescue were among fire and rescue services that held a minute's silence in memory of those who lost their lives.

It tweeted: "Together with fire and rescue services around the country, we will be holding a minute’s silence at 13:46 in memory of all those who lost their lives on 9/11, including the 343 firefighters who died responding to the attacks."

In a defiant message to be played at a memorial event at the Olympic Park in east London on Saturday, the Prime Minister said the threat of terrorism remained but people refused to live their lives in “permanent fear”.

“The fact that we are coming together today – in sorrow but also in faith and resolve – demonstrates the failure of terrorism and the strength of the bonds between us,” Mr Johnson said.

Labour leader Sir Keir, who attended a private memorial service in the September 11 Memorial Garden in Grosvenor Square in London on Saturday, said the consequences of the attacks were “still being felt to this day”, adding the tragedy was “still so raw”.

He said: “But as we mark this anniversary I’m convinced our resolve has never been stronger.

“We will continue to fight terror and violence, by promoting our values of justice and peace.”