Italy says it will seize two migrant rescue ships in the Mediterranean, citing doubts over their legal status.
Italian authorities said the Lifeline and Seefuchs, operated by the German migrant rescue group Mission Lifeline, were "illegally" flying the Dutch flag.
The Lifeline is carrying 226 migrants rescued off the coast of Libya, Mission Lifeline said.
Separately, the UN refugee agency has reported that 220 migrants drowned in the same area in recent days.
It called for "urgent action" from EU countries.
Why is Italy seizing the ships?
Italy's new right-wing government has taken a harder stance on rescue ships bringing large numbers of migrants to Italy, which is often the nearest port for those rescued off coast of Libya.
Italy's Infrastructure Minister Danilo Toninelli said the ship had broken the law by taking the migrants, even though the Libyan coastguard had already intervened to rescue them.
He said Italy would seize both the Lifeline and the Seefuchs to determine their legal status, and said Italy would "once again save the migrants".
Interior Minister Matteo Salvini initially said in a post on Facebook that the two NGO ships should "go to Holland", as it was said to be flying under a Dutch flag, and should not dock in Italy.
Whether or not the ship is Dutch is the subject of some debate. The Dutch delegation to the EU said in a tweet that the ships are not registered in the Netherlands, and not flying under its flag.
Mission Lifeline, however, later posted an image on Twitter of a registration document it says proves the ships sail under the Dutch flag.
The group also tweeted that it had carried out another rescue overnight, though details of how many migrants were accepted- and by which ship - have yet to be released.
The NGO's co-founder, Axel Steier, denied breaking any laws and defended his organisation's actions.
"In this situation you can't wait," he said. "If you have a rescue you prevent people from dying, from drowning and then you have to make the decisions. You can't wait until someone has a port for you - you have to act immediately."
Mr Salvini remained undeterred, writing in a Facebook post on Friday morning that Malta should accept the Lifeline and its passengers - and reiterating that the ship should be seized, reports BBC.