Italian authorities have detained the Ocean Viking migrant rescue vessel for 20 days over its alleged failure to follow a prescribed route after rescuing dozens of people off the Libyan coast, the ship's operator said Sunday.

"Ocean Viking is detained under the 'Piantedosi Decree-Law' for the second time in two months, punishing humanitarian rescuers for carrying out the lifesaving work that European States fail to do in the central Mediterranean," SOS Mediterranee, based in the French city of Marseille, said on X.

It said the ship had been ordered to return directly to the Italian port of Bari after picking up 244 people in three rescue operations, including 18 unaccompanied minors and four children under the age of four.

But as it was heading for Bari the Ocean Viking received an alert of at least 70 migrants needing help around 15 nautical miles (28 kilometres) from its position, though in fact the skiff was around 60 nautical miles away.

"Without any indication that another ship was en route to help these people in distress, we simply had no other choice, legal or moral, to respond to this alert -- any other choice would have been a violation of international law," SOS Mediterranee told AFP.

In the end the Viking was not in a position to help and resumed its course toward Bari. It did not say if the migrants were later rescued.

On November 15, Italian authorities had already ordered the ship detained for 20 days and issued a fine of €3,300, saying it had failed to coordinate its actions with the authorities.

Since January 2023, 2,678 migrants have disappeared while trying to cross the Mediterranean for Europe, according to the UN's International Organization for Migration (IOM).

Alarm Phone: Six separate boats in central Mediterranean

In a number of posts on social media, migrant rescue hotline Alarm Phone said that it was aware of at least six separate boats crossing the Mediterranean as of Sunday night. 

"We lost contact to 4 boats but are still in contact with 2 boats. Authorities are alerted - rescue is needed!" the NGO said in a post.