Interior Minister Matteo Salvini did not allow an Italian coastguard vessel carrying migrants to dock until European Union countries agreed to take them in.
The coastguard vessel Gregoretti rescued the migrants from two boats off Malta and was awaiting orders where it could take them.
“I will not give permission for them to disembark until Europe commits to accept all the immigrants on board,” Salvini, head of the far-right League party, said in a statement.
Rome asked Brussels to co-ordinate migrant redistribution between member states, a European Commission spokeswoman said, adding the EU executive would act to this effect.
Salvini, also deputy Italian prime minister, staked much of his political credibility on a drive to halt migrant flows and has drawn protests by closing Italian ports to charity rescue ships.
Last August, he prevented another national coastguard boat carrying 150 migrants from docking for five days until Albania, Ireland and Italy’s Catholic Church agreed to take responsibility for them.
Italian magistrates placed the interior minister under investigation for kidnapping, but the upper house Senate blocked the probe, ruling Salvini should benefit from parliamentary immunity.
As Italy shut its ports to migrants, Malta agreed to take in some 143 people its armed forces rescued in two separate operations.
The United Nations refugee agency (UNHCR) feared around 115 would-be migrants drowned in a shipwreck off Libya as they tried to reach Europe in a wooden fishing boat.