"We are at a stage of hope and hopelessness at the same time and will not speculate beyond the facts as we know them," he added.
Earlier, the Argentine navy had insisted that the submarine was in good condition and had passed system safety checks before setting off on a training mission 10 days ago, according to the media reports.
ARA San Juan had only about 10 days of oxygen supply at the outside.
The ARA San Juan last made contact with naval authorities on 15 November.
Reports of a sudden, violent sound detected underwater near the last known position of the vessel suggest it might have imploded after reporting an electrical problem.