(CNN) -

Syria's most dangerous chemical weapons have been destroyed at sea, almost a year after nerve gas killed 1,000 people, including children, in a Damascus suburb, Secretary of State John Kerry said in statement Monday.

The U.S. government container ship, the Cape Ray, spent the last 45 days in international waters destroying 600 metric tons of chemical weapons in an on-board process that neutralizes the chemicals, according to the OPCW, the Organisation for the Prohibition of Chemical Weapons, which led the mission to remove and destroy the weapons

Last August horrific pictures of children killed by nerve gas in a Damascus suburb sparked international condemnation of Syrian government forces and sparked President Obama to declare that the regime of Bashar al Assad had crossed the "red line."

By September, U.N. inspectors said they found evidence that Sarin gas was used in the chemical attack.

The U.N. Security Council, with Russian backing, then passed a resolution requiring Syria to eliminate its chemical weapons arsenal, and al-Assad promised to adhere to the resolution. The following month, Syria began dismantling its chemical weapons program.

"Today, we mark a milestone in our unrelenting work to ensure the end of the Assad regime's deadly chemical arsenal," Kerry said.

He also used the occasion to blast the Syrian government which has been waging a civil war since 2011.

"The Assad regime's brutality must come to an end," Kerry said. "Assad lost any legitimacy to lead Syria long before he gassed his own people to death."

Defense Secretary Chuch Hagel called the captain of the Cape Ray, to "congratulate the ship's crew on finishing their unprecedented work," Pentagon Press Secretary Rear Adm. John Kirby said in a statement.