Still, Croatian media report of 50 more buses on the way, which could further erode already troubled bilateral relations. Out of some 7,000 migrants that crossed into Slovenia since Saturday, some 50 requested asylum.

The government has scheduled an emergency meeting for the evening. Slovenia's capacities can handle 2,500 a day, according to the government.

The migrants have been slowly crossing into Austria, most of them at the Šentilj and Gornja Radgona border crossings, where Austrian authorities accepted a total of almost 1,500 people, Austria's daily limit.

By noon, some 3,000 people entered Slovenia. The biggest group, some 1,800 people, arrived in Slovenia by train, crossing over at the Središče ob Dravi border crossing in the middle of the night.

It took the authorities the entire day to process the group, which waited out in the cold and rain. By the end of the day, all but some 400 had been transported to refugee centres up north.

Amnesty International (AI) issued a protest over the treatment of migrants at the Središče ob Dravi crossing. The Red Cross representatives meanwhile said that some 500 volunteers have been mobilised and additional 400 were on standby.

UNHCR representative for Central Europe, Caroline Van Buren, said that processing of migrants was slower than optimal and that the UNHCR would check whether the police were really doing the best they couldt.

Slovenian officials were meanwhile very critical of Croatia, saying the neighbour was completely uncooperative, failing not only to meet Slovenia's requests about the number of migrants but also to inform Slovenia about its plans on how many migrants would be moved north and to which border crossings.

The Novo mesto Police Administration said in the afternoon that Croatia brought - without any warning to Slovenia - a train with some 1,300 migrants to the vicinity of the Rigonce border crossing and brought another 500 to the vicinity of Obrežje crossing by buses.

The groups entered Slovenia on foot and were brought to the Brežice refugee centre. Local authorities expressed concern in the face of the refugee influx and the overcrowded centre.

The situation was also brought to the attention of the European Commission, which called on Slovenia, Croatia and Hungary to cooperate in the border control.

The Commission is also examining the compliance of the countries' measures in dealing with the refugee crisis with the EU rules.

The government has scheduled a meeting for the evening, with Foreign Minister Karl Erjavec saying beforehand the cabinet would adopt measures to protect the border.

Meanwhile, President Borut Pahor said that Slovenia would step up the control of its border with Croatia if Austria decided to introduce stricter border control.

Morever, Interior Ministry State Secretary Boštjan Šefic told the press that Slovenia was in preliminary talks with countries willing to help it protect its borders. He however rejected claims by opposition Democrats (SDS) head Janez Janša that Germany had offered help in protecting Slovenia's borders.

Janša, who held a press conference, also said that the only way to prevent border crossings of unwanted migrants was by erecting a fence along the border. Šefic meanwhile said that the government was not thinking about this possibility, labelling it as ineffective.