"I can absolutely confirm that he is still alive," Lieutenant Colonel Barry Johnston, spokesman for detainee operations in Iraq, said on Saturday, after reports on Arab television stations that he had died.
"He was alive five minutes ago," he said at about 0310 pm (1210 GMT).
Dubai-based al-Arabiya television said Aziz had died in custody, quoting sources in the International Committee of the Red Cross in Iraq.
Al-Arabiya did not immediately give more details, but Aljazeera quoted sources at the Vatican as confirming the death of Aziz, who was the only Christian member of Saddam's cabinet.
One of 55 former Iraqi officials posted on a most-wanted list by US-led forces after their invasion, Aziz, 68, surrendered in April last year and has been in US custody since then.
"We cannot confirm the death of Tariq Aziz. We have no information on the matter"
Red Cross spokeswoman
In Amman a spokeswoman for the Red Cross said: "We cannot confirm the death of Tariq Aziz. We have no information on the matter."
Meanwhile, Aziz's son told a contact in Rome his father was alive, the Italian news agency Ansa said.
The son, Ziad, got in touch with a French monk and friend of the family, Jean Marie Benjamin, from Amman to say his father was still alive, Ansa added.
Benjmain is understood to have good contacts with the family.
If he is indeed alive, it will be the second time that Aziz has wrongly been reported killed. In March 2003 reports saying he had been shot dead while trying to enter the Kurdish north of the country were quashed when he appeared on TV to tell the world he was alive and well.