The EU's top migration official says an Austrian plan to cap asylum-seeker numbers is unlawful.

Dimitris Avramopoulos said in a letter Thursday that "Austria has a legal obligation to accept any asylum application that is made on its territory or at its border."

The letter to Austria's interior minister, seen by The Associated Press, said imposing a ceiling on asylum-seekers "would be plainly incompatible with Austria's obligations" under EU and international law.

Interior Minister Johanna Mikl-Leitner said Wednesday that Austria would allow no more than 80 migrants a day to apply for asylum at southern border crossing points.

Avramopoulos also warned Mikl-Leitner that Austria should not allow people to travel through the country if their aim is to apply for asylum elsewhere.