"We are on standby for an evacuation of the detained tugboat crew by all possible means," he told Rai 3 television.
Armed men, including one who claimed to be the harbour master, detained the crew comprising eight Italians, two Indians and one Ukrainian and were holding them on board the 75-metre ship, officials and media reports said.
"This is a delicate situation which the harbour master's office and the foreign ministry are monitoring. When they ask us to intervene, we will do so, but that does not depend solely on the defense ministry," La Russa said.
Foreign Minister Franco Frattini said it was unclear why the men had been seized but that Rome did not exclude a kidnapping.
"We don't know what are the intentions of the men who seized the 11 crew members yesterday, but we cannot exclude a kidnapping," the minister said during a telephone call to an Italian television programme.
The ANSA news agency quoted sources as saying the action occurred yesterday afternoon shortly before French warplanes launched air strikes at the start of a Western military operation against Libyan strongman Muammar Gaddafi's forces.
The tugboat was discharging Libyan employees of the Libyan oil firm NOC at the time.
A crisis team of the Italian foreign ministry was monitoring the situation and was in touch with the tugboat's owner, August Offshore, a company based in the southern Italian port of Naples that specialises in assisting oil rigs as well as exploration and production activities.