By September 30, the United States will destroy the last declared chemical weapons in its arsenal, which include the nerve agent GB and date back to the First World War (1914-1918).

The weapons will be destroyed at a military facility in the state of Kentucky, as part of a decades-long campaign to put an end to the stockpiles that have been stored since the end of the Cold War in the 1990s, the Department of Defense has announced.

The US must eliminate its remaining chemical weapons under the International Chemical Weapons Convention, which came into force in 1997 and has been signed by 193 countries.

The munitions now being destroyed in Kentucky are the remains of 51,000 M55 rockets with GB nerve agent - a deadly toxin also known as Sarin - that have been stored since the 1940s.

By destroying these munitions, the US is recognizing that this type of weapon is not acceptable on the battlefield, in a message intended to reach the few countries that have not joined the agreement, according to military experts quoted by Lusa.

Chemical weapons were used for the first time in modern times in the First World War (1914-18), where it is estimated that they killed at least 100,000 people.

Although their use was later banned by the 1949 Geneva Convention, countries continued to keep the weapons until the treaty ordered their destruction.

In the US, almost 800,000 chemical munitions containing mustard agent have been stored since the 1950s in heavily protected concrete bunkers.

In the operation now taking place in Kentucky, the most problematic munitions were sent to an armored stainless steel detonation chamber to be destroyed at around 593 degrees Celsius.

The US states of Colorado and Kentucky were the last among several others, including Alabama, Arkansas, Oregon and Utah, where US chemical weapons were stored and destroyed.