9/11 victims honoured at Ground Zero on 15th anniversary of terrorist attacks

The United States has commemorated the 15th anniversary of the 9/11 attacks with a moment of silence observed in a sombre remembrance service at Ground Zero in New York, where nearly 3,000 people were killed.

"Our diversity, our patchwork heritage, is not a weakness. It is still and always will be one of our greatest strengths," he said.At another remembrance service at the Pentagon, US President Barack Obama urged Americans to embrace the nation's diversity and not to allow "terrorists" to divide the country.

"This is the America that was attacked that September morning. This is the America that we must remain true to."

US presidential candidates Hillary Clinton and Donald Trump temporarily paused their bitter election campaign to attend the service with police and relatives of the victims at the September 11 memorial.

"We'll never forget the horror of September 11, 2001," Mrs Clinton said in a brief statement.

"Let's honour the lives and tremendous spirit of the victims and responders."

Mr Trump said in a statement that it was a day of sadness and remembrance, but also of resolve.

"Our solemn duty on behalf of all those who perished ... is to work together as one nation to keep all of our people safe from an enemy that seeks nothing less than to destroy our way of life," he said.

The moment of silence was observed at 8:46am (local time) — the time when the first hijacked passenger jet hit the North Tower of the World Trade Centre.

It was the first of six moments of silence that will be observed in the Big Apple.

Ceremonies were also planned at the Pentagon, where another jet struck.

More than 340 firefighters and 60 police were killed on the sunny Tuesday morning in 2001, in the worst attack on US soil since Pearl Harbor was bombed in 1941.

Many of them died while running up stairs in the hope of reaching victims trapped on the towers' higher floors.

In his weekly radio address on Saturday, Mr Obama said it had been one of the darkest days in the history of the nation, but that it underlined the core values and resilience that define Americans.

"We're still the America of heroes who ran into harm's way; of ordinary folks who took down the hijackers; of families who turned their pain into hope," Mr Obama said.

"We are still the America that looks out for one another, bound by our shared belief that I am my brother's keeper, I am my sister's keeper."