Juncker was speaking after Turkish Prime Minister Ahmet Davutoğlu warned that he will tear up the controversial EU-Turkish migrant deal unless his citizens are given visa-free access to the EU in June, in a move which will put further pressure on EU leaders.
"As part of the agreement, we are working towards visa liberalization for Turkish citizens. Turkey must fulfill all remaining conditions. Visa liberalization is a matter of criteria. The criteria will not be watered down in the case of Turkey," Juncker said.
Under the deal, arriving in Greece after March 20 are being processed in 'hotspots' from where migrants deemed "irregular — not meeting the requirements for asylum — are dispatched back to Turkey in return — on a one-for-one basis — for a Syrian refugee being relocated from Turkey to EU member states.
The deal includes an agreement that all Turks will be allowed visa-free access to EU members states by June 2016.
Divisions Over Turkey
Many relief agencies — including Médecins Sans Frontières, the International Rescue Committee, the Norwegian Refugee Council, Save the Children and Red Cross — have joined the UN Refugee Agency UNHCR in saying the EU-Turkey deal is either immoral or illegal as the 'hotspots' have become detention centers.
Today we present first report on implementation EU Turkey agreement. Progress made,but also at beginning of our work https://t.co/cRgvEXJEh1— DimitrisAvramopoulos (@Avramopoulos) April 20, 2016
As part of the deal, the European Commission said: "The UNHCR will be a key actor in the resettlement process to provide additional support and supervision."
However, only four days after the relocation scheme began, the UNHCR announced it was withdrawing support for the EU-Turkey deal after it said the 'hotspots' in which migrants are being processed in Greece are effective prisons.
"Under the new provisions, these sites have now become detention facilities. Accordingly, and in line with our policy on opposing mandatory detention, we have suspended some of our activities at all closed centers on the islands. This includes provision of transport to and from these sites," UNHCR spokesperson Melissa Fleming told reporters.
Many in Europe have been critical of the EU-Turkey deal as there are fears the visa-free agreement would cause a huge flood of Muslims into the EU bloc.
Part of the deal also includes an acceleration of Turkey's accession to the EU — which is a matter of concern for human rights groups, who say the Turkish Governments is repressing the Kurds, stamping out opposition parties and repressing independent media.