Baghdad , Iraq ( CNN ) -- Saddam Hussein 's cousin Ali Hassan al-Majeed -- also known as Chemical Ali -- was executed Monday , an Iraqi government spokesman said . He was hanged after having been convicted on 13 counts of killings and genocide , Ali al-Dabagh said . Al-Majeed had been sentenced to death in four separate trials , including one that focused on his involvement in a poison gas attack against Iraqi Kurds that killed about 5,000 people . His execution had been delayed for political rather than legal reasons . It is not clear what change , if any , led to the reported execution . Al-Majeed had been held in United States custody since his capture in 2003 . But he was handed over to the Iraqi authorities in the 24 hours before his execution , U.S . Ambassador Christopher Hill told CNN 's Diana Magnay on Monday . The 1988 poison gas attack on the village of Halabja , which earned al-Majeed his nickname , was part of the Anfal campaign , in which the Hussein regime killed at least 100,000 Iraqi Kurds . The campaign is believed to be worst poison gas attack on civilians ever . Al-Majeed was sentenced to death separately for his role in putting down a Shiite uprising against Hussein in 1991 , and for his part in putting down a Baghdad revolt in 1999 . Estimates of the Shiite death toll in the 1991 rebellion range from 20,000 to 100,000 . Al-Majeed was convicted of playing a key part in the slaughter during the revolt in southern Iraq that followed the 1991 Persian Gulf War . One of his co-defendants in the Anfal case , Sultan Hashem , is a prominent Sunni leader who is considered a key player in efforts to reconcile the country 's once-dominant Sunni community with the Shiite majority that now wields political power . Hashem was also sentenced to death , but Iraq 's Sunni Arab Vice-President Tariq al-Hashimi has long refused to sign his execution order . That delayed the execution of al-Majeed and another defendant as well . Iraqi law requires all three members of the Iraqi presidency council -- the president and two vice-presidents -- to sign execution orders . It does not say what happens if they do not sign . CNN 's Yousif Bassil contributed to this report .
NEW : U.S. handed al-Majeed over to Iraqi authorities shortly before execution , official says . Saddam Hussein 's cousin Ali Hassan al-Majeed executed . Al-Majeed had been sentenced to death in four separate trials . Execution had been delayed by VP 's refusal to OK the deal and a dispute with his family about whether he was mentally competent enough for lethal injection.