"We believe that the proposal is impossible to implement and that it represents a setback in relation to the existing solution, which we find bad," Milanovic told reporters in Zagreb on Tuesday, after talks on constitutional changes between government officials and opposition representatives at the government headquarters.

Milanovic said the opposition's initial proposal was to organise voting for members of the diaspora in Croatia's territory, namely at Croatian embassies and consulates. He added that opposition representatives had put forward a number of proposals made by civil society associations, which he said had now been put on the back burner.

The SDP leader recalled that in the last two weeks the opposition had not made any statements on the matter because it wanted to give the HDZ room for internal consultations.

Asked if the opposition had a united position on this issue, Milanovic said that their position was to negotiate patiently, as "this is a very important issue which must be regulated as part of constitutional changes". He said a new round of talks on constitutional changes would be held at the government headquarters on Friday.

The SDP leader said that the only disputable issue that remained to be solved was the model of voting for Croatian nationals without permanent residence in Croatia.

He said that talks were under way to harmonise positions on the referendum issue and on the criteria for its success, adding that the two sides were on track to reaching a good solution that would be in Croatia's interest.

When asked if the opposition was united in its proposals, Milanovic said that the SDP, the Croatian People's Party (HNS), and the Istrian Democratic Party (IDS) believed that the issue of voting of Croatian nationals who do not reside in Croatia should be regulated in a different way which would be easier to supervise and which would be in line with the practice in European countries and the rest of the world.

"In Croatia, this certainly cannot be voting by post because it would lead to situations in which one person votes for five other persons, and we also have to take into account the fact that voter registers have not been ordered," Milanovic said.

Asked if he expected constitutional changes to be adopted soon, he answered that he expected the HDZ to understand that the existing model of out-of-country voting was bad and that it should be changed.

He welcomed the decision to urgently order the Permanent Residence Act and ensure its strict implementation, but added that in the light of recent presidential elections, this should not be viewed as a kind of punishment for Croats, particularly those living in Bosnia-Herzegovina, who he said did not vote in the recent elections the way the HDZ had expected.

Milanovic called for determining, in talks with the Croats in Bosnia-Herzegovina, the financial entitlements which were important to the Bosnian Croats and which, he said, Croatia would be able to finance.

He also said that a just and logical solution and a controllable election system would be insisted on, to the benefit of Croatia and Croats living outside the country, notably those in Bosnia-Herzegovina.