At present some 800 European jihadi fighters have been captured in Syria. Most are held by the Kurds, but Kurdish forces are expected to come under pressure when the US quits the theatre. President Trump has called on the Europeans to take back "their" fighters and prosecute them.
Earlier today Belgian justice minister Koen Geens indicated that a European concerted approach was needed. British and Belgian officials are expected to meet within hours. Mr Michel also intends to contact the Dutch PM and the French president.
Mr Michel and Mrs May also discussed the UK's departure from the EU. Mr Michel insisted the European Single Market was crucial for Belgian jobs and businesses. He added that every effort should be made to avoid a No Deal Brexit on the basis of the withdrawal agreement already reached between the EU and the UK.