European Union states moved towards a two-year suspension of their open-borders zone on Wednesday as the bloc's executive again rebuked them for failing to act on agreements to stem irregular migration.The European Commission, in reports ahead of an EU summit next week when leaders will again discuss how to resolve a crisis that has set them against each other, renewed its pleas for Greece and Italy to speed up the establishment of processing centers to register refugees and deport illegal migrants. Migration Commissioner Dimitris Avramopoulos praised Athens and Rome for a "spectacular" increase in how many arrivals they are fingerprinting but said they were still falling short. He said other member states were also failing to stand by front-line Mediterranean counterparts and take in more than a few hundred asylum seekers from Italy and Greece under an EU scheme that stipulated the relocation of at least 160,000. "We need urgently to shift gears," Avramopoulos told a news conference, saying he had written to each of the bloc's 28 interior ministers spelling out what more they needed to do.The arrival last year of over 1.1 million migrants, many of them refugees from Syria, and their subsequent chaotic overland journeys across Europe, where most have ended up in Germany, has strained the passport-free Schengen zone to breaking point - with numerous member states re-imposing temporary border checks. The European Commission said on Wednesday that returning to internal border controls on a systematic and long-term basis could cost as much as 18 billion euros in total direct costs alone, excluding second-wave effects.In an effort to at least maintain the structure within its legal framework, EU officials and diplomats are working to give governments a legal right to extend temporary internal border checks to which Germany and others resorted as an emergency.The legal basis for some of these expires in mid-May and so the EU has begun a process to trigger an unprecedented use of a longer-term derogation within the Schengen treaty by that time. The Commission ruled that an inspection in Greece found that it was seriously deficient in protecting its section of Schengen's external border, a key condition for allowing other states to then declare a need to impose controls of their own.A Greek government official voiced frustration with the way fellow EU members have treated Greek efforts to cope with the biggest movement of people in Europe since World War Two. The official said: "The blame game must end."Meanwhile, tougher restrictions from Balkan countries may cause thousands of migrants to be stranded in the Balkan route, several reports said. Migrants first sailed to Greek islands then crossed through Balkan countries such as Macedonia, Serbia, Hungary, Croatia and Slovenia, intending to reach Austria and then Germany and other wealthy northern European countries.Last month, Austria set off a wave of responses from countries upstream on the Balkan route, after saying it will limit the influx of asylum seekers to 37,500 this year and a total of 127,500 until mid-2019. Slovenia, Croatia, Serbia and Macedonia - which are between Austria and Greece on the Balkan route - immediately responded with a filter allowing only Syrians, Afghans and Iraqis to pass to the north.Many of the countries along the route are primarily equipped for short-term migrant stays, limiting their ability to take on refugees if the path closes further downstream. Macedonia on Tuesday began reinforcing and expanding a fence along its southern border, with Macedonian authorities setting up a camp for migrants turned back by countries further along the route which are also narrowing the gates to new entries.Serbia's capacity to shelter people for a long period of time would be exhausted within three days at present arrival rates, the U.N. refugee agency UNHCR warned. The 17 existing centers for asylum seekers and migrants in Serbia are equipped only for emergency shelter, not residence, UNHCR officials told the Belgrade daily Danas. If other countries on the route close their gates, Serbia will immediately do the same, Foreign Minister Ivica Dacic said after meeting with Austrian Foreign Minister Sebastian Kurz on Tuesday.The European Union has warned countries on the Balkan route not to take unilateral action. Its executive, the European Commission, said Wednesday that tightening border controls will undermine actions that have been taken to alleviate the migration pressure.The majority of migrants come from the Middle East and Africa. The turmoil in the Middle East and the five-year war in Syria have led many people to flee the conflict in an attempt to seek security and shelter in a more prosperous and peaceful country, such as one in Europe. However, Europe has been slammed for lacking a collaborative response to the crisis.