Europe's migration commissioner says the European Union has made progress on handling migration issues, but more remains to be done and efforts need to be strengthened, particularly in filling gaps in the bloc's border agency.

Speaking in Brussels, Dimitris Avramopoulos noted a significant increase in the number of illegal crossings recorded on the Greek-Turkish border, while stressing the figures were still far below those of the height of the migration flow into Europe.

The EU says 6,108 people have crossed the Greek-Turkish land border illegally so far this year, a nine-fold increase from the same period last year. A further 9,349 arrived by sea on Greek islands from the Turkish coast.

Avramopoulos said the European Commission would not support the building of a fence or wall on the Greek-Turkish border.