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

2:15 p.m.

Europe's leading human rights body is calling on Greece to provide alternatives to detaining children under an agreement between the European Union and Turkey to limit migration.

Several hundred children remain detained at camps on the Greek islands since the agreement took effect in late March.

In a report published Wednesday, the Council of Europe urged Greek authorities to address the issue "urgently" and to follow up on reports that refugee children were involved in criminal activities, including prostitution and drug trafficking.

An envoy from the Strasbourg, France-based body visited refugee shelters at six sites around Greece in March.

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11:20 a.m.

The European Commission says it's ready to start negotiating an agreement with Nigeria to send back Nigerian migrants who do not qualify to stay in the European Union.

The Commission said in a statement Wednesday that the move would ensure that returns are done "rapidly and efficiently." It said the so-called readmission agreement would respect international law.

Around 22,000 Nigerian nationals crossed the Mediterranean Sea to reach Europe last year, according to the EU's border agency, Frontex.

The EU only provides international protection to people fleeing conflict or violence.

EU member states must still give the green light for the readmission talks with Nigeria to begin.