The Latest on the flow of migrants into Europe (all times local):

4:05 p.m.

Slovenia's prime minister says his country has been strengthening border controls — including beefing up metal fences — to prepare for a potential new wave of migration into Europe.

Miro Cerar says an increase in numbers of migrants trying to reach the European Union remains a "realistic possibility and we have to be ready for that scenario."

Cerar said Monday in Serbia migration could swell if an EU deal with Turkey falters or the 28-nation bloc fails to hammer out a united policy on the issue.

He insists: "Europe must remain open and humane for people fleeing grave human rights violations ... but we must also prevent illegal migration."

Countries on the migration route closed borders in March after over 1 million people came in 2015.

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1:30 p.m.

Greek police say dozens of residents in an island camp for refugees and other migrants have set fire to part of the facility that handles asylum applications, during a protest over delays in the asylum process.

Nobody was injured in Monday's riot at the Moria camp on the eastern Aegean island of Lesbos, but three prefabricated cabins used as offices by asylum officials were severely damaged.

Police said about 70 migrants, mainly Pakistani and Bangladeshi nationals, threw stones at the cabins and then set them on fire with burning blankets. Riot police detained 22 suspected rioters.

More than 60,000 refugees and other migrants hoping to move deeper into Europe are trapped in Greece following a series of Balkan border closures. Some 15,000 of these are on the eastern islands.