One day after Germany curbed the freedom of movement in the region by temporarily reinstating border controls, the country's vice chancellor estimated that as many as 1 million refugees may arrive by the end of the year as other nations moved to fortify their frontiers.

The prediction from Sigmar Gabriel, who leads the Social Democrats, underscored how quickly the numbers fleeing to Germany are spiraling upward. The official government estimate, released just a few weeks ago, is for roughly 800,000 in 2015, nearly four times the 2014 figure.

European Union interior and justice ministers will try to bridge a divide over the region's worst refugee crisis since World War II when they meet Monday in Brussels to hammer out an agreement over binding quotas redistributing 160,000 migrants who have flooded into Hungary, Greece and Italy.

Eastern European countries including Poland and the Czech Republic have opposed such measures. Germany, which supports the EU proposal, on Sunday introduced the temporary controls on the southern border with Austria, where thousands of migrants have been crossing into the country.

Austria responded Monday by sending 2,200 troops to its border with Hungary, while Slovakia reinstated checks along its border with both countries.

Critical Gathering

"Of course, the idea is not to prolong this, but it's a short-term measure that should be in place for as short a time as possible," Felix Braz, the justice minister of Luxembourg, which currently holds the rotating EU presidency -- said in an interview. "A lot will depend on what comes out of Brussels this afternoon."

Germany's move risks creating widespread disruption as governments weigh a further tightening of frontier controls across Europe. German Chancellor Angela Merkel will meet with her Austrian counterpart, Werner Faymann, Tuesday in Berlin to discuss the crisis.

"A temporary closing doesn't mean that the border is shut," Steffen Seibert, Merkel's chief spokesman, said Monday in Berlin. "Refugees will continue to come and we hope that it will happen as part of a more orderly process."

The re-imposition of controls abandoned over the past 20 years is a signal to Europe that Germany, the region's biggest economy, needs more help to cope. The sudden move also underscores the risk attached to Merkel's strategy of welcoming refugees while fellow EU leaders stand still. The federal government canceled a planned cabinet retreat this week, and will instead meet with the leaders of the country's 16 states on Tuesday, Seibert said.

Security First

Germany was right to temporarily suspend free-travel rules, three state leaders from Merkel's Christian Democratic Union said before a party meeting in Berlin on Monday.

The move was "definitely needed" because questions of security come first, said Reiner Haseloff, prime minister in the eastern state of Saxony-Anhalt. Hesse state leader Volker Bouffier said: "It has to be made clear to other European states that this can't go on." Saarland premier Annegret Kramp- Karrenbauer said the Schengen open-border agreement "relies on the trust that the external borders are protected."

Refugee Surge

Austria, which also backs the EU's quota plan, will send the troops mainly to the border with Hungary to support police handling the refugee influx, Chancellor Werner Faymann said in Vienna. Germany so far hasn't sent back any refugees, and that Austria, which temporarily shut the main highway between Vienna and Budapest Monday, wouldn't close its border either, he said.

"I expect us to act like Germany, and let in people who're seeking refuge," Faymann said. "Border checks can be tightened temporarily under the Schengen agreement, and police on the borders have shown that they can do that while respecting humanitarian needs. It's a balancing act they've handled well and with which the troops will help them now."

Austria expects as many as 20,000 refugees to enter the country on Monday, mostly at the main crossing in the town of Nickelsdorf, Christian Stella, deputy police chief in the eastern province of Burgenland, told public radio broadcaster Oe1.

Hungary, which is erecting a razor-wire fence along the border with Serbia to keep refugees out, on Tuesday will begin deporting or imprisoning those who try to cross the border illegally, in line with a new law making such acts a crime rather than a misdemeanor, Prime Minister Viktor Orban said.

"New rules that take effect tomorrow will strengthen Hungary's border defense," Orban told police cadets in Budapest on Monday. The prime minister is deploying thousands of soldiers to the border to try and repel a tide of migrants that stream into the European Union country each week.

EU Divisions

Europe's leaders are struggling to form a united front in the face of refugees fleeing conflicts from Syria to Eritrea, Afghanistan and Iraq. In addition to a summer influx from Libya across the Mediterranean, growing numbers of people are traveling from Turkey to Greece and north through the Balkans via Hungary and Austria.

The European Commission, the EU's executive arm, said the German decision to tighten controls "appears to be a situation covered by the rules" of the Schengen agreement eliminating internal borders. The goal must be to go back to open borders "as soon as feasible," it said in a statement.

In an effort to halt human smuggling from Libya, EU governments agreed on Monday to widen a naval surveillance mission in the south- central Mediterranean Sea to enable the search and seizure of suspect vessels.

The launch of the wider mission hinges on when EU governments can supply the added forces. It will be confined to international waters until the United Nations permits the EU to take the fight closer to Libya.