SERBIA, CROATIA - Tensions are rising between Serbia and Croatia as the two countries struggle to deal with the migrant crisis. Croatia and Serbia ramped up a tit-for-tat dispute over border crossings, as the schism over the migrant crisis between the Balkan neighbors and one-time bitter foes deepened into harsher recriminations. The European Union agreed to modest measures to address the crisis at an emergency summit the night before. But the ongoing spat between former Yugoslav republics Croatia and Serbia, which is not an EU member, and an announcement by Austria that it was sending back asylum seekers to other EU countries, made clear that the crisis on the front lines is only growing. Thousands of migrants are pouring into countries on the EU's edges in record numbers in an effort to get to more affluent countries in the West, leaving neighbors at odds over how to maintain control of their borders. During the night, Croatia refused entry to all Serbian cars and citizens trying to cross at the main Bajakovo crossing. The government later allowed people to move, but maintained its ban on vehicles, and extended the ban to another border crossing at the town of Tovarnik. The measures are a direct response to Serbia's decision on Wednesday to ban Croatian cargo traffic, itself a retaliation for Croatia's closure of seven of its eight road border crossings last week. The fight brings relations between the two countries to one of their lowest point since the end of the Balkan wars of the 1990s after the communist collapse. Serbs who wanted to remain in Yugoslavia fought a bloody war to try to stop Croatia from gaining independence, but the two countries have since made efforts to reconcile. Serbia called Croatia's latest move discriminatory. Ratcheting up the rhetoric, the country's foreign minister likened the measure to rules enforced when Croatia had a puppet government controlled by Nazi Germany and Italy. Serbia's Prime Minister Aleksandar Vucic called Croatia's steps "irrational and stupid." More than 44,000 people have entered Croatia from Serbia since last Wednesday, and the Croatian government is attempting to divert the influx by pressuring its counterparts in Belgrade to direct the migrants eastward, toward Hungary and Romania. This pushed the total for this year to 242,093. The previous daily record for Hungary was 9,380 people, who arrived from Serbia on Sept. 14, just before Hungary built a razor-wire fence along the Serbian border. Hungary's Prime Minister Viktor Orban said Wednesday he was considering allowing migrants to pass freely to Austria and ultimately Germany. Mr. Orban has for months tried to discourage migration through Hungary, building the fence, deploying police and authorizing the use of the army. As of Wednesday, a record 10,000 people passed through Hungary between its borders with Croatia and Austria. Austrian Interior Minister Johanna Mikl-Leitner said on Thursday that Austria began sending back asylum seekers who had registered in another EU country, where they should await asylum decisions. More than 5,000 have already been sent back, primarily to Bulgaria and Romania, and more people will be moved back to Croatia and Serbia, she said. To try to keep people away, Hungary has also placed advertisements in the Middle Eastern press, saying in English and Arabic that the country wouldn't welcome people entering its territory without valid passports and visas, and warning them they would be prosecuted if they tried. EU leaders on Wednesday agreed on policies aimed at reducing the numbers of migrants who seek to enter the bloc. These included more money for Syria's neighbors to help settle and integrate refugees from the war-ravaged country, including up to €1 billion ($1.1 billion) for Turkey, and more money for the EU border and asylum offices. The plans also call for setting aside more money for the EU countries most affected by the influx of people seeking refuge on the continent. The summit followed weeks of fighting over a mandatory plan to relocate 120,000 asylum seekers already in Europe. That was settled Tuesday when interior ministers took the unusual step of forcing some smaller countries, including Hungary, into the plan.