Iraq has executed Ali Hassan al-Majeed, the Saddam Hussein henchman widely known as "Chemical Ali", for crimes against humanity, government spokesman Ali al-Dabbagh said.

"The death sentence against Ali Hassan al-Majeed has been carried out," Dabbagh said.

Majeed, a cousin of Saddam's who earned his nickname because of his use of poison gas, was executed by hanging, the government said in a statement.

He had received four death sentences, the last about a week ago for an attack on the Iraqi Kurdish town of Halabja in which thousands were killed.

Dabbagh said in a statement that Majeed was not subjected to any abuse during the execution, unlike when Saddam was hanged in December 2006.