ATHENS—Protests against Greek government plans to build camps for refugees and other migrants escalated on Monday, further testing Greece’s ability to meet European Union demands to control the massive inflow of people via the Aegean Sea.

Residents on the Aegean island of Kos, where locals and riot police have been clashing daily since Friday, blockaded an army camp where the government wants to build a migrant registration and screening center, preventing construction work.

Protesters in Athens, including members of the neo-Nazi Golden Dawn party, demonstrated against a transit camp for migrants near the port of Piraeus. Work has also been blocked on a northern Greek transit camp near Thessaloniki since Sunday because of a protest by local residents.

Greek Prime Minister Alexis Tsipras’s government is struggling to set up a string of migrant registration centers by mid-February, before a scheduled EU summit, to show that Greece is safeguarding the bloc’s border against uncontrolled migration and should remain part of Europe’s passport-free-travel Schengen zone. Some EU governments have stepped up pressure on Greece and suggested that it should be suspended from the 26-country Schengen area if it can’t better manage the flow of migrants.

Greece has promised to build the so-called hot spots on the islands of Lesbos, Kos, Samos, Chios and Leros, where large numbers of migrants are arriving by boat from the nearby coast of Turkey. EU authorities want Greece to screen those arriving, separating refugees from economic migrants who don’t qualify for asylum in Europe.