Ahead of an expected White House announcement, McConnell said that the Blue Grass Army Depot, a US Army facility in Kentucky, had recently completed its four-year job of eliminating some 500 tons of lethal chemical agents, the last batch held by the US military.

The US had held for decades stores of artillery projectiles and rockets that contained mustard and nerve gases and blister agents.

"Chemical weapons are responsible for some of the most horrific episodes of human loss," McConnell said in a statement.

"Though the use of these deadly agents will always be a stain on history, today our nation has finally fulfilled our promise to rid our arsenal of this evil," he said.

Other signatories to the 1997 Chemical Weapons Convention had already eliminated their holdings, Fernando Arias, head of the Organization for the Prohibition of Chemical Weapons (OPCW), said in May.

That left only the United States to complete the task, he said.

"More than 70,000 tons of the world's most dangerous poisons have been destroyed under the supervision of the OPCW," he said.