By Wisam Mohammed BAGHDAD, Nov 30 (Reuters) - The Iraqi government has asked U.S. President George W. Bush to order the handover of Saddam Hussein's cousin, known as "Chemical Ali", and two other former officials convicted of genocide, so they can be executed. Saddam's cousin Ali Hassan al-Majeed, former Defence Minister Sultan Hashem and former army commander Hussein Rashid Muhammad are being held in U.S. military custody while officials argue over who has the authority to transfer them for execution. They were convicted of genocide for their roles in a campaign against Iraq's Kurds in 1988, but the U.S. military has said it will not hand them over until it receives what it calls an "authoritative government of Iraq request". What constitutes such a request is at the centre of a row between Prime Minister Nuri al-Maliki's Shi'ite-led government and President Jalal Talabani, a Kurd, and Sunni Arab Vice President Tareq al-Hashemi. Government spokesman Ali al-Dabbagh told Reuters on Friday Maliki had sent a letter to Bush last week in which he "demanded the three convicts be handed over". "The U.S. forces do not have the right to interfere in a (judicial) case and decide whether it was legal or not," Dabbagh said. "Only Iraqi authorities have the right to do so." The U.S. embassy in Baghdad had no comment on the letter. Maliki has said the U.S. embassy in Baghdad has played an "unfortunate role" in preventing the handover of the three. Talabani and Hashemi say Iraq's constitution stipulates that the three-man presidency council -- made up of the president and two vice presidents -- should sign the order. Maliki's government says the council has no such right. His letter to Bush indicates his government's impatience to carry out the sentence, which was upheld by an Iraqi court in September. Under Iraq's constitution, the death sentence should have been carried out within 30 days. Hashemi has threatened to resign if the government goes ahead with the executions without a presidential decree. He said he narrowly stopped the government from executing them in September. The legal dispute has been complicated by a growing chorus of calls for Hashem's life to be spared. Many Sunni Arabs say he was a soldier simply following the orders of Saddam's feared cousin al-Majeed, known as "Chemical Ali". Dabbagh recently told foreign journalists the Iraqi government "understood" those who wanted to reduce Hashem's sentence but stressed the need to find a legal way to resolve the impasse. He said the issue should not be politicised. In 1988, Hashem was commander of Task Force Anfal, which targeted Kurdish areas in northern Iraq in a military campaign that killed tens of thousands and destroyed entire villages. His supporters say he was simply a figurehead. Saddam was hanged on Dec. 30 after being found guilty in a separate trial that was not subject to the same legal wrangling. (Writing by Alaa Shahine; editing by Philippa Fletcher)