Hungary's Prime Minister Viktor Orban warned at the United Nations that Europe will be "destabilized" if the mass flows of migrants and refugees continue unabated.
Hungarian Prime Minister Viktor Orban aims to meet UN chief Ban Ki-moon in New York this week ahead of a possible closure to thousands of migrants of the EU country's border with Croatia.
US President Barack Obama pressed European nations to take their "fair share" of refugees, after the EU reluctantly reached an agreement designed to halt a destabilizing humanitarian crisis.
Slovakia's leftist Prime Minister Robert Fico said he would rather risk infringing EU rules than implement mandatory refugee quotas adopted by the bloc.
Greek Prime Minister Alexis Tsipras, who returned to power after Sunday's election, called for "shared" European responsibility in tackling the migrant crisis facing the bloc.
Four eastern EU states opposed to fixed migrant quotas across the bloc said they were "absolutely dedicated" to reaching an agreement with western partners on solving Europe's worst migrant crisis.
Hundreds of migrants gathered on Croatia's main border crossings with Slovenia on Saturday, seeking transit through Slovenian territory in their bid to travel to northern Europe.
German Foreign Minister Frank-Walter Steinmeier said that EU members reluctant to accept migrant quotas may have to be outvoted and overruled in the 28-member bloc.
The European Union has announced an emergency summit in Brussels next in a bid to find solutions to the continent's worst refugee crisis since World War II.
Thousands of migrants arrived in Croatia early seeking to open up a new route to northern Europe, after Hungary sealed its border, sparking ferocious clashes with angry refugees.
EU president Donald Tusk said he would consider requests by German Chancellor Angela Merkel and others for an emergency summit on migrants and decide later this week.
Hungary plans to build a fence to keep migrants out along part of its border with Romania in addition to the barrier being erected along the frontier with Serbia.
Hungary's populist prime minister called for a massive aid package to be given to countries around war-wracked Syria to help stem the flow of migrants to Europe.
Tens of thousands of people marched through London in protest against Britain's refugee policy, with new Labour Party leader Jeremy Corbyn attending in his first political engagement only hours after being elected.