It is important that member-states' ministers have backed the initiative and efforts aimed at solving the border dispute and removal of the blockade of Croatia's accession negotiations, Rehn said after notifying ministers of his proposal.
In his statement to the Finnish media, Rehn said he hoped that Slovenia and Croatia would show more cooperativeness.
The commissioner expects responses from both Slovenia and Croatia to his latest initiative until Monday evening and he is to hold talks with the Croatian and Slovene foreign ministers, Gordan Jandrokovic and Samuel Zbogar, in Brussels next Wednesday.
Details of the latest initiative are still unknown. This Finnish politician said that it was a very detailed proposal elaborated by legal experts.
Rehn declined to comment on an idea by Austrian Foreign Minister Michael Spindelegger on separating the border demarcation from the issue of Slovenia's right to have access to the high seas.
Rehn said that Croatia still could wrap up the EU accession negotiations by the end of this year provided that the blockade of its entry talks is lifted in a foreseeable time and Croatia continues reforms, notably in the judiciary and shipbuilding industry.
Commissioner Rehn's activities are supported but the time is running out and we cannot wait indefinitely, said the Czech Deputy Prime Minister in charge of European affairs, Alexandr Vondra.
Asked to comment on the Austrian minister's idea about separating the issue of border demarcation from Slovenia's access to the high seas, Vondra said that he did not think that those two things could be forever kept together, and stressed that they must be separated.
Slovene Minister Zbogar was quoted by the Ljubljana-based Delo daily on Saturday as saying that his country will not unblock its eastern neighbour's EU talks as long as there is no result of the European Commission's mediation.
The Slovene official persists in refusing a possibility for the two countries to engage the International Court of Justice to solve their bilateral problem.
He also refuted comments that Slovenia was being exposed to pressure from the EU due to its veto of Croatia's accession negotiations, according to Delo.