BRUSSELS (Reuters) - The number of migrants reaching the European Union by sea fell by two-thirds in 2016 due to a migration deal with Turkey but arrivals in Italy from north Africa hit an all-time high, the EU said on Friday.

The deal concluded in March provides Turkey with billions of euros as long as it keeps refugees on its territory and stops people smugglers from moving them across the Aegean to Greece.

It also involved promises to Ankara of financial aid, visa-free travel to much of the EU and accelerated membership talks, which have all been put on hold because of Turkey's crackdown on critics after a failed military coup last July.

Migrants still making the journey across the western Mediterranean mainly came from Syria, Afghanistan and Iraq, the EU's border agency Frontex said.

Some 181,000 migrants arrived in Italy in 2016 from north Africa through the so-called central Mediterranean route, the highest number ever recorded and 20 percent more than last year, it said.

The largest group of migrants arriving in Italy were Nigerians, Eritreans and Guineans, the agency added.

The International Organization for Migration had said previously that 2016 was the deadliest year for migration in the Mediterranean with almost 5,000 deaths. [nL5N1EP25I]

(Reporting by Robert-Jan Bartunek; Editing by Tom Heneghan)