ROME - Italian authorities engaged in another standoff with a humanitarian NGO vessel in the Mediterranean on Thursday, even as the EU backed down on a proposed reform that irked Italy to the point where Prime Minister Giuseppe Conte said he might not take part in a migration pre-summit in Brussels on Sunday.

It began with a tweet from Mission Lifeline, a German NGO. "We are currently rescuing 300 to 400 people," the German NGO tweeted early on Thursday. "Reinforcement by the Italian Coast Guard or merchant ships is required."

Italian interior minister Matteo Salvini, who leads the far-right League party and also serves as deputy prime minister, reacted with a video on Facebook.

In it, he accused the Mission Lifeline vessel of "forcibly embarking 224 illegal immigrants", saying that "the only way this ship of pseudo-volunteers...will see Italy is on a postcard".

Earlier this month, Salvini made international headlines when he turned away the Aquarius, another NGO migrant rescue ship with 629 people on board. The rescue ship docked in Spain instead.

Italian transport minister Danilo Toninelli followed up on prime minister's Tweet, claiming on Facebook that the Mission Lifeline vessel operated in Libyan waters "in violation of international law".

"The law of the sea does not allow unregulated ships to navigate," Toninelli said.

Meanwhile, Italy appeared to score a major point when the European Union (EU) backed down on a draft document that had circulated ahead of a pre-summit on migration and asylum this Sunday in Brussels.

The draft reportedly emphasized the need to stop migrants from traveling within the EU and speeding up procedures to send them back to the country where they first arrived -- which is usually Italy.

This prompted Conte to suggest he would snub the meeting. However, on Thursday, German Chancellor Angela Merkel put a stop to this possibility with a phone call to Conte.

"I confirmed to her that it would have been unacceptable for me to take part in the pre-summit (to debate) a prefabricated text," Conte wrote on Facebook.

"The Chancellor said there had been a misunderstanding, and that the draft document released yesterday will be set aside."

The pre-summit was called by European Commission chief Jean-Claude Juncker ahead of a European Council summit on June 28 and 29, when a reform of the Common European Asylum System (CEAS) will feature prominently on the agenda.

Italy's proposal at the pre-summit may include opening "European protection centers" to process asylum claims in migrant countries of origin and transit, Italian news agency ANSA reported, citing government sources.

Italy, Greece, and Spain have borne the brunt of the migration crisis, as tens of thousands of men, women and children fleeing war and destitution in Africa and the Middle East entrust their lives to migrant traffickers to illegally ferry them across the Mediterranean.

Italy's new right-wing, populist coalition government has taken a hardline stance on immigration, as promised on the campaign trail.