The EU's migration commissioner has warned it would be "unacceptable" for countries to refuse proposed refugee sharing quotas, setting up a fresh row with eastern European states that oppose the plan. Dimitris Avramopoulos told AFP in an interview that agreement on quotas is "reachable" by a June deadline -- despite longstanding opposition from eastern states. EU interior ministers meet in Sofia on Thursday to discuss asylum reforms that have been blocked for over a year because of disagreement over migrant quotas that would kick in in case of a new crisis. Former communist countries including Hungary, Poland and the Czech Republic vehemently oppose compulsory quotas, arguing they can meet their obligations by contributing funds to overburdened Italy and Greece, the EU entry point for most migrants. "This is unacceptable," Avramopoulos, who is Greece's EU commissioner, said when asked if a settlement could emerge by June in which some member states refuse to admit refugees. "It is a shared responsibility. All countries should be part of our policy to share the burden of this heavy pressure," he added, dismissing the idea of making financial contributions to Italy and Greece as an "arbitrary interpretation" of solidarity. Bulgarian officials have said it will be difficult to reach agreement on the topic by June, the deadline set by EU leaders -- and the end of Sofia's presidency of the bloc. But Avramopoulos said: "Everything is reachable. What is a prerequisite is a strong political will to be shared by all member states." - 'Urgent' action needed - The EU took Hungary, Poland and the Czech Republic to court in December for refusing to accept quotas for asylum-seekers. Eastern states have been opposed ever since other EU states adopted by majority a temporary quota system in 2015 as a form of solidarity with Greece and Italy during the height of Europe's migrant crisis. Under the plan, asylum seekers are relocated to other members of the bloc in a temporary exception to the so-called Dublin rules, which requires countries where they first land to process them. The EU has since stalled on plans for a permanent mechanism for future crises amid resistance from the eastern countries. Hungary has led eastern opposition to refugees and migrants, saying the region will not be able to integrate them and it will face a security threat, particularly from Muslims. "It is very urgent to move forward in adopting a new Dublin," said Avramopoulos, a former Greek foreign minister and mayor of Athens. "What we need now is a strong well-balanced, and fair Dublin." "It has to be defended because without solidarity Europe cannot exist," Avramopoulos said. - EU future threatened - "Today it is Italy and Greece that are under huge pressure but nobody can assure us that the future is not holding some surprises in other parts," he said. He said the division over how to deal with the worst migration crisis since World War II posed a greater threat to the European project than economic worries. Migration, he said, "is directly linked to the principle of values upon which Europe is built". In December, Avramopoulos denounced as "anti-European" a letter from European Council President Donald Tusk that suggested abandoning the quotas because they were "ineffective" and "highly divisive." Tusk's council groups the member states, while Avramopoulos serves on the European Commission, the EU's executive arm which first pushed the quota system. Avramopoulos was unrepentant about his comments, saying: "What I said at this moment was said because I felt that these statements were undermining our European strategy on very important issues." The commission said the scheme was effective as it had 32,000 people relocated, or 90 percent of those eligible. The scheme was originally meant to relocate 160,000 refugees.