Buenos Aires, Nov 25 (IANS): The Argentine submarine that went missing nine days ago while heading northward from the country's southern tip was not on a secret mission and authorities have no reason to believe the vessel was attacked, the Navy has said.

"The submarine was sailing from Ushuaia to Mar del Plata on a direct route inside the exclusive economic zone, near the edge, exercising the monitoring of sovereignty as any other Navy unit does," Captain Enrique Balbi said at naval headquarters in Buenos Aires on Friday.

Headquarters last heard from the ARA San Juan on the morning of November 15, when the sub was located in the San Jorge Gulf region some 432 kilometres east of the Argentine coast.

"It was not on a secret or special mission. There is no indication of any attack or anything similar," the Navy spokesman said.

In Mar del Plata, the sub's home port, some 350 people, including friends and family of the San Juan's 44-member crew, mounted a procession from the city's Our Lady of Lourdes cathedral to the naval base to honour the missing sailors and pray for their safe return.

"The truth is that we are bad at this moment. At the beginning we had hope ... but we still have hope!," one of the participants said.

The procession came amid growing discontent among the families of the crew after they learned that an explosion was detected near the sub's last known location on the day contact was lost.

More than a dozen nations are assisting Argentina in the search for the San Juan, which was built in Germany in 1983 and refurbished a few years ago.

The government announced the start of an investigation to "determine the degree of responsibility and non-compliance within the chain of command" and said that the current naval command would be dismissed once the submarine was found.