Thousands of refugees waited for hours in the rain before entering Croatia, as officials struggled with a growing backlog. Slovenia has capped the number of arrivals, triggering a domino effect across former Yugoslavia.
Some 6,000 people were stuck in the mud-drenched no man's land between Serbia and Croatia, before Croatian border police let them through late Monday.
The refugees waited in the rain for hours when "without any announcement, the borders opened. When the borders opened, everybody rushed" over, said UNHCR spokesman Melita Sunjic.
Earlier in the day, Slovenian border police turned away more than 1,000 refugees arriving from Croatia, prompting Zagreb to slow its pace of taking in refugees, which created a growing backlog of migrants across the Balkans.
"It's like a big river of people, and if you stop the flow, you will have floods somewhere. That's what's happening now," Sunjic said at the Berkasovo-Bapska crossing.
Migrants fought among themselves after a night in the open on the Serbian side, aid workers said.
Tempers fray between neighbors
Slovenian authorities accused Croatia of breaking the deal to stem the immigrant flow heading to richer EU countries.
Some 5,000 refugees arrived across the Croatian border on Monday, double the number Slovenia was ready to accept in a day, authorities said.
"Croatia is ignoring our pleas, our plans," the state secretary at Slovenia's interior ministry, Bostjan Sefic, told a news conference.
"Yesterday, the Croatian side stopped answering our phone calls, so we do not know how many migrants to expect, which is making our work very difficult," Interior Minister Vesna Gyorkos Znidar said on Monday.
Her Croatian colleague Ranko Ostojic rejected the accusations, saying instead that Ljubljana kept changing the terms.
"Slovenia first said it could receive up to 8,000 migrants (daily), then 5,000, then 2,500 and now it has been reduced to zero. It would mean that the whole burden is being left to Croatia," he said.
He added that Croatia would not allow itself to become a "migrant collection center" for the EU, and accused Greece of failing to stem the flow of tens of thousands into Europe from Turkey.
EU 'turning its gaze'
Some 10,000 immigrants entered Serbia from Macedonia on Sunday, according to UNHCR officials.
After Slovenia and Croatia started holding back new arrivals, Serbia's minister in charge of migration also suggested his country may try to curb the flow from Macedonia.
"We have to think about how many people we can take in under such conditions," Aleksandar Vulin told reporters in Berkasovo. "Let's not blame Serbia when the entire EU is turning its gaze from what's happening here."
dj/msh (Reuters, AP, dpa, Beta)