An ad questioning what really happened on 9/11 that appeared on Ottawa city buses Wednesday has sparked outrage and prompted the city's transit commission to order a review of its advertising policy.

The ad, which focuses on why World Trade Center Building 7 collapsed when it was not hit by a plane, is part of a campaign called ReThink911 sponsored by well-known 9/11 'Truther' organization Architects & Engineers for 9/11 Truth.

The group suggests that Tower 7 collapsed due to a controlled demolition and subscribes to a theory that there has been a government "cover-up" about what really happened on September 11, 2001. The group wants a new independent review regarding the attacks.

The group says the campaign in Ottawa consists of 300 posters.

Ottawa transit commisioner Diane Deans said Wednesday that "to have those ads running on buses seems, at the very least, insensitive," according to CBC News. Deans said she is ordering a review of OC Transpo's advertising policy, but said the right to free speech must be considered.

The ads, which are also running in several major U.S. cities, on a major Toronto billboard and in Vancouver transit shelters, have sparked widespread outrage.

The Toronto billboard is in Yonge and Dundas square, often compared to New York's Times Square.

Andres Acero, an Ottawa bus rider who spread a photo of the ad, told the Ottawa Citizen they are "disrespectful and callous."

Another rider, Adam Toner, told the Citizen that he understands the free speech argument, but that "to have something like that on the anniversary, that's a little disrespectful to families, friends who lost somebody there."

Not everyone is angry about the ad.

Kirk Lowry, a passerby in Yonge and Dundas Square, told The Toronto Star he's "suspicious of people instantly debunking something as not true. I will look it up, there are oddities."

U.S. President Barack Obama marked the 9/11 anniversary from the White House Wednesday.

"Our hearts still ache for the futures snatched away, the lives that might have been," Obama said.

The attack on the World Trade Center towers, the Pentagon and United Flight 93 in 2011 killed 2,977 people, not including the 19 hijackers.

Related on HuffPost:

Loading Slideshow...
  • Unforgettable 9/11 Images

    In this Sept. 11, 2001 file photo, United Airlines Flight 175 approaches the south tower of the World Trade Center in New York shortly before collision as smoke billows from the north tower.

  • Unforgettable 9/11 Images

    A hijacked commercial plane approaches the World Trade Center shortly before crashing into the landmark skyscraper Sept. 11, 2001 in New York.

  • Unforgettable 9/11 Images

    Hijacked United Airlines Flight 175 from Boston crashes into the south tower of the World Trade Center and explodes at 9:03 a.m. on September 11, 2001 in New York City.

  • Unforgettable 9/11 Images

    Pedestrians on the waterfront in Brooklyn, New York, look across the East River to the burning World Trade Center towers Sept. 11, 2001 after a terrorist attack.

  • Unforgettable 9/11 Images

    A helicopter flies over the Pentagon in Washington, Tuesday, Sept. 11, 2001 as smoke billows over the building. The Pentagon took a direct, devastating hit from an aircraft and the enduring symbols of American power were evacuated.

  • Unforgettable 9/11 Images

    Smoke comes out from the Southwest E-ring of the Pentagon building September 11, 2001 in Arlington, Va., after a plane crashed into the building and set off a huge explosion.

  • Unforgettable 9/11 Images

    Officials examine the crater Sept. 11, 2001 at the crash site of United Airlines Flight 93 in Shanksville, Pennsylvania.

  • Unforgettable 9/11 Images

    Photo dated Sept. 11, 2001 shows US President George W. Bush being informed by his chief of staff Andrew Card of the attacks on the World Trade Center in New York during an early morning school reading event in Sarasota, Florida.

  • Unforgettable 9/11 Images

    A person falls from the north tower of New York's World Trade Center Tuesday Sept. 11, 2001 after terrorists crashed two hijacked airliners into the World Trade Center and brought down the twin 110-story towers.

  • Unforgettable 9/11 Images

    The south tower of New York's World Trade Center collapses Tuesday Sept. 11, 2001. In one of the most horrifying attacks ever against the United States, terrorists crashed two airliners into the World Trade Center in a deadly series of blows that brought down the twin 110-story towers.

  • Unforgettable 9/11 Images

    In this Tuesday, Sept. 11, 2001 file photo, people run from a cloud of debris from the collapse of a World Trade Center tower in New York.

  • Unforgettable 9/11 Images

    A firefighter breaks down after the World Trade Center buildings collapsed September 11, 2001 after two hijacked airplanes slammed into the twin towers in a terrorist attack.

  • Unforgettable 9/11 Images

    This September 11, 2001 file photo shows Marcy Borders covered in dust as she takes refuge in an office building after one of the World Trade Center towers collapsed in New York. Borders was caught outside on the street as the cloud of smoke and dust enveloped the area. The woman was caught outside on the street as the cloud of smoke and dust enveloped the area.

  • Unforgettable 9/11 Images

    A man with a fire extinguisher walks through rubble after the collapse of the first World Trade Center Tower September 11, 2001, in New York. The man was shouting as he walked looking for victims who needed assistance.

  • Unforgettable 9/11 Images

    An unidentified woman reacts moments after watching both of the nearby World Trade Center towers collapse Tuesday, Sept. 11, 2001, in New York. She was among the residents of the nearby Battery Park City apartment complex waiting to be evacuated from the area.

  • Unforgettable 9/11 Images

    In this Tuesday, Sept. 11, 2001 file photo, rubble and ash fill lower Manhattan streets after two hijacked airliners were crashed into the towers of the World Trade Center in New York, collapsing them. (AP Photo/Boudicon One)

  • Unforgettable 9/11 Images

    This NASA Landsat image taken on Sept. 11, 2001 shows that the damage and smoke from the terrorist attacks could be seen from space.

  • Unforgettable 9/11 Images

    A view of the remains of an ambulance in front of the Millenium Hotel at Ground Zero after the collapse of both towers of the World Trade Center following the terrorist attacks on September 11, 2001 in New York, New York, USA.

  • Unforgettable 9/11 Images

    The rubble of the World Trade Center smoulders following a terrorist attack Sept. 11, 2001 in New York.

  • Unforgettable 9/11 Images

    Firefighters raise a U.S. flag at the site of the World Trade Center after two hijacked commercial airliners were flown into the buildings September 11, 2001 in New York.

  • Unforgettable 9/11 Images

    The sky glows orange as the sun rises over the damaged side of the Pentagon with the US Capitol behind in Washington, DC, 13 September, 2001.

  • Unforgettable 9/11 Images

    U.S. President George W. Bush speaks to rescue workers, firefighters and police officers from the rubble of Ground Zero September 14, 2001 in New York City.

  • Unforgettable 9/11 Images

    Photo dated Sept. 11, 2001 shows firefighters making their way through the rubble of the World Trade Center in New York after two hijacked planes flew into the landmark skyscrapers.