France, Germany and the U.S. observed Syria's deadly use of chemical weapons on civilians one year ago in the town of Khan Sheikhoun by vowing to hold accountable those who were responsible.

In an early morning attack on April 4, 2017, Syrian aircraft dropped sarin gas bombs on the town, killing scores of people, including several children.

A still image taken from a video posted to a socia FILE - A still image taken from a video posted to a social media website on April 4, 2017, shows people lying on the ground, said to be in the town of Khan Sheikhoun, after what rescue workers described as a suspected gas attack in rebel-held Idlib, Syria. FILE - A still image taken from a video posted to a social media website on April 4, 2017, shows people lying on the ground, said to be in the town of Khan Sheikhoun, after what rescue workers described as a suspected gas attack in rebel-held Idlib, Syria.

A joint statement issued Wednesday by the U.S. State Department on behalf of French Foreign Minister Jean-Yves Le Drian, German Foreign Minister Heiko Maas, U.K. Foreign Secretary Boris Johnson and U.S. Acting Secretary John Sullivan said, "... there has been no let-up in the atrocities committed by the Syrian regime, enabled by its backers," after seven years of war.

They blamed Russia for reneging on a promise to ensure Syria would stop using chemical weapons by voting in November to close a U.N. Security Council investigation into Syria's use of the weapons.

"We are committed to ensuring that all those responsible are held to account," the statement continued. "We will not rest until in our efforts to seek justice for the victims of these abhorrent attacks in Syria."

Human Rights Watch marked the year-old attack Wednesday by declaring that global efforts to prevent chemical attacks in Syria have failed. It also said evidence from its investigation and a probe by the U.N. suggests the Syrian regime was responsible for the attack.

"In Syria, the government is using chemical weapons that are banned the world over without paying any price," said Human Rights Watch Middle East director Lama Fakih.

The rights group said since Russia vetoed a U.N. resolution to renew an investigation, the Syrian regime has probably carried out at least five additional chemical weapons attacks.