The European Commission is due to unveil its latest version of a controversial plan to force EU member states to more evenly absorb the wave of migrants reaching Europe via the Mediterranean.
UN chief Ban Ki-moon was also due in Brussels on Wednesday after urging Europe to do more to help migrants and after the EU has sought UN Security Council approval to launch a naval operation against migrant smugglers.
The commission, the executive of the 28-nation EU, will ask member states to share the burden of admitting tens of thousands of asylum seekers who land in Italy, Greece and Malta, the AFP news agency reported.
"The proposal is not perfect, but it amounts to an enormous step forward, because it introduces the principle of solidarity," EU foreign policy chief Federica Mogherini said on Tuesday.
"We will have to build a consensus" around the relocation proposal for asylum seekers "so that interior ministers can approve it" by a simple majority when they meet June 16 in Luxembourg, she added.