Migrants are staging demonstrations at four sites around Greece, to protest delays in asylum procedures promised under a European Union agreement with Turkey.

Around 500 migrants chanting "open the borders" gathered Thursday in Greece's second largest city, Thessaloniki.

Protests were also held on the islands of Chios and Lesbos, while scores of migrants at a camp near the Greek-Macedonian border blocked the main highway linking the two countries for about 30 minutes.

Police announced no arrests.

Some 60,000 migrants remain stranded on Greece's mainland and the islands since European border closures earlier this year.

Under the EU-Turkey deal, migrants who arrived in Greece after March 20 can be deported back to Turkey.