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.
The task is bound to be particularly difficult because Britain, Hungary, the Baltic states, the Czech Republic and Poland oppose mandatory relocation based on a redistribution "key" system.
European governments have been forced to act after hundreds of migrants trying to reach Europe in rickety and overcrowded boats died in the past one month in the Mediterranean, including the drowning of up to 900 on a single vessel.
Warning of 'emergency'
The proposal by EU Home Affairs Commissioner Dimitris Avramopoulos suggests migrants be distributed according to four criteria: gross national product, population, unemployment and the number of asylum requests already registered in the country.
The relocation plan is to allow for the transfer to other states of people eligible for international protection. It opens a breach in the Dublin rules that require the country where asylum seekers first land to take them in.
The measure aims to respond to an "emergency," according to the commission, which fears the arrival of a wave of migrants and asylum seekers during the summer in Italy, Malta and Greece.
Around half a million migrants could attempt to cross the Mediterranean, the UN International Maritime Organization warned in late April.
The effort to share the burden is due to be limited in time and concerns only new arrivals from the month of July.
EU nations already approved plans May 18 for an unprecedented naval mission starting next month to fight human traffickers responsible for a flood of migrants crossing the Mediterranean from Libya.
The scheme backed by foreign and defence ministers in Brussels will involve European warships and surveillance aircraft gathering intelligence and then raiding boats to crack down on people smugglers.
But the EU is still waiting for a UN resolution that will allow it to destroy boats that belong to people smugglers in Libyan waters.