In pictures: United States commemorates 9/11 anniversary

The US paused on Thursday to mark the 13th anniversary of the September 11 attacks. The ceremonies came just hours after Barack Obama told the country he had authorised stepped-up air strikes against ISIS. Here's a gallery of photos from the memorial service.

The United States marked the 13th anniversary of the Sepember 11 attacks against a troubling backdrop. The ceremonies came just hours after President Barack Obama told the country he is authorizing stepped-up airstrikes in Iraq and Syria against Islamic State extremists. In New York City, family and friends of those who died read the names of the 2,983 people killed there, at the Pentagon and near Shanksville, Pennsylvania.

In Washington, Obama observed a moment of silence outside the White House with the first lady and Vice President Joe Biden before heading to the Pentagon's 9/11 memorial. “Thirteen years since the peace of an American morning was broken,” the president said, speaking to family members of victims and a few survivors. “Thirteen years of moments they would have shared with us.”

Here's a gallery of photos from Thursday's commemoration.

People look at the 'Tribute in Lights' illuminated over lower Manhattan during events marking the 13th anniversary of the 9/11 attacks on the World Trade Center in New York. (Reuters)

The 'Tribute in Lights' is reflected on the 9/11 Memorial on September 11, 2014 in New York City. This year marks the 13th anniversary of the September 11th terrorist attacks that killed nearly 3,000 people at the World Trade Center, Pentagon and on Flight 93. (AFP)

A red balloon floats in the air as onlookers have their photograph taken in front of the "Tribute in Light" illuminated over the Lower Manhattan skyline on the 13th anniversary of the 9/11 attacks. (Reuters)

A rose is left at the 9/11 Memorial on September 11, 2014 in New York City. (AFP)

Roses and flags left by loved ones are placed on the names inscribed at the North Pool during memorial observances on the 13th anniversary of the Sept. 11 terror attacks on the World Trade Center in New York. (AP)

Eileen Esquilin hugs her husband, Joe Irizarry, while mourning the loss of her brother, Ruben Esquilin Jr, during the memorial observances held at the site of the World Trade Center in New York. (AFP)

Sam Pulia, mayor and a former police officer of Westerchester, Ilinois, mourns over the name of his cousin, New York firefighter Thomas Anthony Casoria, who was killed in the South Tower, prior to the the memorial observances held at the site of the World Trade Center in New York. (AFP)

Several hundred motorcyclists gathered on the National Mall for a rally to honor the survivors and first responders of the 9/11 terrorist attacks September 11, 2014 in Washington, DC. (AFP)

US President Barack Obama (C), First Lady Michelle Obama (L) and Vice President Joe Biden (R) arrive for a moment of silence on the South Lawn of the White House in Washington, DC to mark the 13th anniversary of the 9/11 attacks on the United States. (AFP)

US President Barack Obama speaks at the Pentagon in Washington, DC during a ceremony marking the 13th anniversary of the 9/11 attacks on the United States. (AFP)

Obama listens to the national anthem during a ceremony to mark the 13th anniversary of the 9/11 terrorists attacks that killed nearly 3,000 people at the World Trade Center, Pentagon and on Flight 93. (AFP)

US President Barack Obama (L), First Lady Michelle Obama and Vice President Joe Biden (R) observe a moment of silence on the South Lawn of the White House in Washington, DC on September 11, 2014, the 13th anniversary of the 9/11 attacks. (AFP)

A view shows a portion of the 2,977 flags laid out to signify the people who lost their lives in the 9/11 attacks during a remembrance event on the campus of Cuyamaca College in El Cajon, California. (Reuters)

First lady Michelle Obama listens during a ceremony marking the 13th anniversary of the 9/11 attacks at the Pentagon in Washington September 11, 2014.

A man looks up at One World Trade Center near the 9/11 Memorial site on the 13th anniversary of the 9/11 attacks on September 11, 2014. (Reuters)

A gallery staffer checks a display by Spanish photographer Angel Marcosto that shows images of the US's World Trade Center building before and after the terror attack, during ArtRio, the annual international art fair in Brazil. (AFP)

A man photographs One World Trade Center (reflected center) near the 9/11 Memorial site on the 13th anniversary of the 9/11 attacks in New York, September 11, 2014. (Reuters)

Meanwhile, members of the "9/11 Truth" movement protest near the 9/11 Memorial on the 13th anniversary of Al Qaeda's attack on the United States. (Reuters)

U.S. Secretary of Defense, Chuck Hagel, listens during the Pentagon Community September 11th Observance, a remembrance ceremony to mark the 13th anniversary of the terrorist attacks at the Pentagon in Arlington, Virginia. (AFP)

People walk past the work of artist Mr. Brainwash as he creates a massive 9/11 Mural across the street from the The National September 11 Memorial & Museum on the 13th anniversary of the September 11, 2001 attacks. (AFP)

A woman lays flowers at the Fire Department of New York (FDNY) Memorial Wall on September 11, 2014. (AFP)

A US soldier holds photographs of the September 11, 2001 attacks in remembrance of those who perished thirteen years ago during the 9/11 attacks, at a military base in Bagram, 50 kms north of Kabul on September 11, 2014. (AFP)

A man visits a bench, which represents a victim during the 9/11 Pentagon attack, prior to a ceremony to mark the 13th anniversary of the terrorists attacks at the Pentagon Memorial. (AFP)

A woman hugs a boy during the memorial observances held at the site of the World Trade Center in New York, September 11, 2014. (AFP)

A motorcyclist gathered on the National Mall for a rally to honor the survivors poses in front of a memorial on September 11, 2014 in Washington, DC. (AFP)

A rose is left behind in remembrance of those lost after the memorial observances held at the site of the World Trade Center in New York, September 11, 2014. (AFP)