The EU on Thursday pledged more money for Italy's work with Libya to stem migrant flows to Europe, with Brussels seeing a "real chance" to close the central Mediterranean route.

Italian Prime Minister Paulo Gentiloni has been working with his UN-backed Libyan counterpart Fayez al-Sarraj to sharply reduce the perilous migrant sea crossings to Italy, the main entry point to the European Union.

"Leaders agreed to offer Prime Minister Gentiloni stronger support for Italy's work with the Libyan authorities," EU President Donald Tusk said at a summit of the bloc's 28 leaders in Brussels.

"We have a real chance of closing the central Mediterranean route," Tusk told a press conference, after officials reported earlier this month that the numbers of migrant departures from Libya have dropped 20 percent so far this year.

The EU sealed a deal with Turkey last year that has slowed to a trickle migrant and asylum seeker flows across the Aegean Sea to Greece, which was the main entry point to Europe at the migration crisis's peak in 2015.

Tusk said EU heads of government and state decided at the summit to "provide sufficient finances" for north Africa under a two-year-old trust fund set up for economic development.

The pledge comes with an assurance by the European Commission, the bloc's executive, that "this money is channeled to stem illegal migration," the former Polish premier said.

Italy has played a major role in training Libya's coastguard to stop migrant smuggling in its territorial waters while carrying out stop, search and rescue operations on the high seas.

European Commission President Jean-Claude Juncker, standing next to Tusk, again lashed EU member countries for having fallen way short of their duty to contribute to the Africa trust fund.

"Member states so far have committed 175 million (euros). This is clearly not enough," the former Luxembourg prime minister told the press conference.

During a summit with their African counterparts in Malta in November 2015, EU leaders agreed to set up a trust fund underpinned by 1.8 billion euros from the common EU budget.

Member states are supposed to match that amount, but Juncker said the commission had increased its share to 2.5 billion euros, then to 2.9 billion and lately to 3.1 billion euros to make up part of the shortfall.

"We are reaching our limits," Juncker added.

More than 1.6 million migrants have entered Europe by sea since 2014 in the biggest such crisis since World War II. More than 13,500 have died on the way.