Migrants arrive by boat at the Sicilian harbour of Pozzallo, February 15, 2015. [Photo/Agencies]

On Sunday, a speedboat carrying four people armed with Kalashnikov rifles approached a coast guard cutter carrying out a rescue, Italy's transport minister Maurizio Lupi said.

The armed people threatened the mariners to let them take back and re-use the migrants' boat, Lupi said, "another terrible development in the horrendous trafficking of men, women and children in the Mediterranean".

Italy had only made vague statements about willingness to lead a UN mission in Libya until Friday, when Gentiloni said it was "ready to fight" there.

Prime Minister Matteo Renzi, who has long called for more help from the EU to deal with migrants and for UN intervention in Libya, told RAI TV in an interview on Saturday: "The problems cannot all be left to us because we are the first, the closest, the people who pick up the boats."

Italy's anti-immigrant Northern League party has made a rallying cry out of the migrant arrivals, which numbered more than 160,000 last year.