ATHENS — An agreement between the European Union and Turkey to deport migrants on Greek islands back to the Turkish mainland is to take effect Monday morning.

Giorgos Kyritsis, a spokesman for the Greek government’s refugee crisis committee, said Frontex, the EU’s border management agency, is solely responsible for the implementation, adding that only a fraction of its promised personnel of more than 2,000 is in place.

Frontex has secured three vessels that will make the short trip from the island of Lesbos to the Turkish coast starting Monday morning.

It aims to deport about 750 migrants, mostly from Pakistan and Afghanistan, who did not apply for asylum or whose applications were rejected, in the first three days.

In a separate development, Italian demonstrators clashed with Austrian police on Sunday when they crossed the Brenner Pass border to protest against Austria’s plans to enforce controls to limit the passage of migrants.

Some 500 human rights activists marched on the border Sunday, lighting flares and spraying ‘‘Welcome’’ on a sign announcing the passage to Austria. Austrian police said they detained around 50 protesters for throwing stones at officers, injuring five, and vandalizing property. Police used batons and pepper spray to drive back the protesters, according to reports.

An Austrian official was also quoted in the German media as saying that Austria will deploy soldiers to the borders to ensure that an expected influx through Italy won’t make it north.

Associated Press