BRUSSELS (Reuters) - Temporary border controls inside the European Union s free-travel zone could be extended for up to three years during a crisis, the European Commission proposed on Wednesday, giving it more leeway to stem migration. The proposal by the EU executive comes as border controls in Germany, Austria, Denmark, and Norway expire, part of the European Union s response to a surge of refugees and migrants in November 2015 that tested EU rules on passport-free travel. Those countries must lift the frontier checks by November this year under a two-year-limit set by the bloc in the so-called Schengen area, which is named after a town in Luxembourg and aims to be a symbol of free movement in the bloc.  While not referring to the four countries, the Commission s plan, if agreed by EU governments, would allow them to keep the controls in place for another year if they can justify them. EU home affairs commissioner Dimitris Avramopoulos said the threat of migrants coming through Greece and the Western Balkans was no longer a valid excuse for frontier checks.  No internal border control ... in relation to those from the eastern Mediterranean will be possible after November,  Avramopoulos told a news conference.  All member states maintain the possibility to introduce internal border controls for other threats to their internal security,  he said, stressing those  must remain exceptional.  Germany has long argued it needs the controls to combat the threat of Islamic militancy in Europe. The EU has taken in more than 1.7 million people from the Middle East and Africa since 2014. But after a mass influx in 2015, numbers have gone down steadily following a 2016 deal that closed the route from Turkey to Greece. The EU has also stepped up support for Libya to curb arrivals in Italy. Sweden has lifted its border checks but has stepped up internal controls. Norway is part of Schengen but not the EU. 