The Latest on Europe's migration crisis (all times local):

1:20 p.m.

Serbian police say they have arrested eight people for smuggling migrants across the border to Hungary.

Police said Monday they are suspected of organizing accommodations, transfers and the smuggling of seven illegal migrants from Turkey and Syria to Hungary for 5,250 euros ($5,910).

Human trafficking has soared in the Balkans as nations have closed down their borders recently to migrants hoping to reach the European Union after fleeing war and poverty at home.

Hungary last year built a razor-wire fence along its southern border with Serbia, but smugglers still guide migrants through the holes in the wire or over the fence. Migrants are also hidden in trucks or in overcrowded vans — and many end up being double-crossed by the smugglers and never reach their destinations.

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1 p.m.

Monitors from Turkey have arrived on the Greek islands of Lesbos and Chios to help supervise an agreement aimed limiting the number of refugees flowing into the European Union via smugglers' boats.

The officers arrived Monday and were to stay for at least one week, as Greek authorities scrambled to implement the landmark deal reached last week between the EU and Turkey that includes faster refugee relocations to European countries as well as collective deportations of migrants from Greek islands back to Turkey.

Greece's conservative opposition criticized the Turkish arrivals, a controversial topic as Greece and Turkey have ongoing boundary disputes in the Aegean Sea.

Government figures released Monday said the number of stranded refugees in Greece exceeded 50,000 with no significant letdown in the number of daily arrivals.