Some EU members have raised concerns ahead of talks on whether asylum seekers could be processed outside the bloc in so-called "transit camps".
The Italian island of Lampedusa is a target for illegal immigrants
Spain has said care must be taken to ensure Europe does not "allow itself any moral backward steps".
A plan envisages setting up processing centres - notably in North Africa - where cases would be considered.
Meanwhile, more than 400 more suspected illegal immigrants have landed on the small Italian island of Lampedusa.
They arrived on two separate boats during the night. Their precise countries of origin are not clear, though some are said to be from Africa and the Middle East.
Under the plan expected to be put forward by Germany during the two-day meeting of European ministers on Thursday and Friday, those crossing into the EU illegally by sea would also be taken to the new centres.
Some EU states are likely to mount strong opposition to the plan. The UN refugee agency has also cast doubts on the proposal.
The agency says it is unclear if such a system could guarantee people's basic rights.
Spanish Interior Minister Jose Antonio Alonso said: "We must be very sure that the initiative will respect the human rights of refugees, their dignity as human beings."
The idea of transit camps was first proposed by Britain 15 months ago, and the German government is now expected to revisit the proposal.
On the eve of the two-day meeting of EU interior and justice ministers, German Interior Minister Otto Schily urged his colleagues to back the plan.
"We are jointly of the opinion that the conditions in the Mediterranean call for a solution that stops illegal immigration," Mr Schily told the home affairs committee of the German parliament.
"We have to stop people coming to Europe illegally, risking their lives. We need to work out a concept that has the joint backing of the EU," he said.
Germany and also Italy - which is a springboard for many illegal immigrants to get into the EU - are the key forces behind the asylum camp plans, the BBC's Geraldine Coughlan in The Hague reports.
The idea is to have processing centres, possibly in countries such as Tunisia or Libya, where asylum-seekers could go in the first place, or be taken to after being picked up on the high seas, correspondents say.
That is different from the original British proposal - which had been to remove at least some asylum-seekers within the EU.
Opposition to any such plan is likely to be intense, our correspondents say.
Many countries within the 25-member EU remain unconvinced.
The plan has also been criticised by organisations such as the UN and Amnesty International.
They say that the camps would face insurmountable financial, logistical and legal problems.