Argentine naval base Commander in Mar del Plata Gabriel Attis told relatives of over 40 crew members of the submarine on Saturday that the ARA San Juan has been recently found deformed and with signs of the explosion.
"As a tribute to all of them [the crew], we declare a three-day mourning," Macri said in a statement.
The president also expressed gratitude to all the countries involved in the search operations.
The Argentinian authorities resumed the search for the submarine in late October after signing a contract with Ocean Infinity. The US seabed intelligence company is known for conducting the search operation for the missing MH370 Malaysian airliner. Ocean Infinity has reportedly committed to receiving payment from Argentina only if ARA San Juan is found.
The submarine with over 40 crew on board went missing after reporting about a technical malfunction. The search and rescue operation for the submarine involved equipment and personnel from various countries, including Russia.