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

3:20 p.m.

Serbia's customs officers have discovered three migrants from Afghanistan hidden in two cargo trucks with Macedonian license plates that were heading toward the European Union.

Customs authorities said the migrants were discovered early Monday at the Serbian border with EU-member Croatia. Two migrants were hiding in a truck bound for Italy, while the third one was in a truck heading to Germany.

Authorities said that the customs officers looked into the trucks after their drivers suspected someone had climbed into them when they stopped earlier at a nearby gas station.

Migrants fleeing war and poverty have been looking for ways to enter the EU countries illegally after countries closed their borders for free entry in March. Thousands remain stuck in the Balkan countries.

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2:10 p.m.

The Organization for Economic Cooperation and Development is urging governments to improve reception conditions for migrants in order to address anti-immigration backlash.

In a report on international migration released on Monday, the Paris-based international organization recommended countries address the local impact of the arrival of migrants.

The OECD said "large and sudden" inflows of migrants are often concentrated in the most disadvantaged areas and that governments should scale up public services in those areas.

The organization is also suggesting that countries step up international cooperation and is urging the international community to "significantly increase its effort in terms of resettlement".

Migration flows increased by 10 percent in 2015 across the OECD area, which is made up of 35 leading industrial countries from all around the world.

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12:55 p.m.

Several dozen refugees have staged a protest in an asylum center in Slovenia, complaining that the EU nation is slow in processing their asylum requests.

The refugees gathered outside the asylum center in the capital Ljubljana on Monday, holding a banner reading "We are Human Beings." They are demanding a meeting with Slovenia's interior minister.

The refugees have also complained over what they described as bad living conditions in the center. One migrant told Slovenia's public broadcaster that "these are not normal conditions."

Hundreds of thousands of refugees and migrants passed through Slovenia last year at the height of Europe's migrant crisis. Slovenia and other countries along the route closed their borders for migrants in March.

Slovenian police say 321 refugees and migrants remain in the Alpine country.