Italy's far-right interior minister has threatened to deport 177 migrants back to Libya if Brussels refuses to redistribute them across Europe in a move that would violate global law.
"Either Europe decides to seriously offer Italy some concrete help, beginning with, for example, the 180 immigrants on board the Diciotti ship, or we will be forced to do what will definitively stop the smugglers' business".
The letter follows threats by Italian Interior Minister Matteo Salvini to send the migrants back to Libya - which the European Union has said is not a safe harbour.
Italian media report that the ship is on its way to Pozzallo.
Malta did not aid a boat carrying 190 migrants crossing global waters - the Italian coastguard vessel Diciotti picked it up after the boat neared the Italian island of Lampedusa. But Malta refused, saying that the migrant boat wasn't in distress and that the migrants declined help from Maltese authorities, preferring to continue toward Italy.
In a tweet on Sunday, he accused Italy of rescuing the migrants in Maltese waters "purely to prevent them from entering Italian waters".
Mr Salvini has continually refused to allow ships with rescued migrants into Italy since a populist coalition started leading the country in June.
If he did return the migrants to Libya, he would be breaking worldwide law which prevents asylum seekers from being returned to a country where they would be in danger of persecution.
Italian Transport Minister Danilo Toninelli accused Malta of shirking its responsibility by not rescuing stricken vessels making the risky journey from North Africa.
"The EU needs to step forward and open its ports to solidarity, otherwise it has no reason to exist".
Numerous human rights abuses have been reported in detention centres that hold migrants hoping to make the perilous crossing of the Mediterranean and arrive in Europe.
His brash talk was followed by that of Italy's hard-line Home Affairs Minister Matteo Salvini, who threatened to take the migrants back to Libya if the European Union did not step in.
Malta's refusal to take in the migrants has infuriated the Italian government, already angered by an operation that Salvini says was carried out by the Italian coastguard without the approval of Rome.
But with the Diciotti blocked outside the port of Lampedusa, Toninelli this morning upped the ante on Malta, insisting that Diciotti's actions showed that Italy never reneged on its duty to save lives at sea.