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

12:10 a.m.

The head of Bulgaria's border police has ordered an investigation into the possible involvement of border officers in the smuggling of 60 migrants at the Bulgarian-Turkish border.

CCTV footage leaked in local media showed the group walking over the border from Turkey on Dec. 29. The infrared camera footage shows them crossing the border line while several people, believed to be border policemen, stay close without taking any action to stop them.

An interior ministry spokeswoman said an ongoing investigation is seeking establish the identity of those standing near the scene. She said that the 60 migrants were detained hours later by police some 20 kilometers (12 miles) inside Bulgarian territory. They did not have any documents.

Signals are mounting that Bulgaria might be affected to a bigger extent by the migrant crisis after the Western Balkans route has been closed, following an agreement between the EU and Turkey.

Bulgaria has not seen floods of migrants since 2013, when it became, alongside Greece, one of the first European states to see a rise in migratory pressure. It has been avoided partly due to stepped-up security measures at the border, but also because of numerous reports of violence, abuse and pushbacks of migrants by police officers.

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11:50 a.m.

The U.N. refugee agency says it's suspending some operations in Greece because centers known as "hotspots" to handle an influx of migrants "have now become detention centers" under a European Union deal to send back some to Turkey.

UNHCR spokeswoman Melissa Fleming says the refugee agency opposes mandatory detention. She said UNHCR would also halt transport to and from the centers.

She said UNHCR is concerned that Greece doesn't have sufficient structures in place to process migrants properly.

The EU-Turkey deal, in which many people who cross the Aegean will be returned to Turkey, took effect over the weekend.

Separately, UNICEF expressed its frustration over the EU-Turkey plan for making no mention of children, who make up 40 percent of people stranded in Greece.