The European Union and Turkey agreed on a deal to stem the migrant crisis, including a three-billion-euro ($3.2-billion) aid package for Syrian refugees in Turkey.
Eurogroup chief Jeroen Dijsselbloem warned that a small group of EU countries may be forced to form a "mini-Schengen" if the bloc fails to resolve its migrant crisis.
Dutch Prime Minister Mark Rutte defended an EU cooperation deal with Ukraine as vital for European stability only months before a referendum Dutch eurosceptics have forced on the accord.
European Union president Donald Tusk called for calm after Turkey, a candidate for membership of the bloc, shot down a Russian war plane on the Syrian border.
Brussels will remain at the highest possible alert level on Monday with schools and metros closed over a "serious and imminent" security threat similar to the Paris attacks.
The European Union agreed to rush through reforms to the passport-free Schengen zone by the end of the year amid growing concerns about border security in the wake of the Paris attacks.
European Commission chief Jean-Claude Juncker insisted that Britain would not leave the EU, as leaders prepare to discuss David Cameron's reform demands at a summit next month.
European Commission President Jean-Claude Juncker firmly defended Sunday the EU's hotly-contested plan to redistribute refugees across Europe despite calls by Poland to scrap the scheme after the deadly attacks in Paris.
Top EU official Donald Tusk warned it would be "very, very tough" to reach a deal on reforms Prime Minister David Cameron has asked for to help keep Britain in the bloc.
EU leaders were considering holding a summit with Turkish President Recep Tayyip Erdogan later this month to seek his help in curbing migrant flows to Europe.
Tens of thousands of protesters poured into Warsaw's streets for a demonstration organised by the far-right, marching under the slogan "Poland for the Polish" and burning an EU flag.
EU regulators have given Volkswagen 10 days to clarify its own admission that nearly a million of the company's cars emit more CO2 pollution than originally claimed.
Prime Minister David Cameron said he was confident of achieving four key objectives in renegotiating Britain's EU relationship but warned the UK would have to "think again" about membership if they were not met.
EU leaders will push their wary African counterparts to help tackle the migration crisis at a summit in Malta this week, offering them billions of euros in aid in exchange for cooperation
The EU's economic affairs commissioner, Pierre Moscovici, voiced confidence that Greece would reach a "compromise" with its creditors by the end of the week on remaining reforms demanded under its third bailout.
EU president Donald Tusk urged Turkey to show its readiness to work with Brussels on issues such as the migrant crisis following a stunning election win by the party of President Recep Tayyip Erdogan.
Eurogroup chairman Jeroen Dijsselbloem said the fallout from the refugee crisis should be considered when assessing some members' budgets, adding it had already had a major impact on debt-ridden Greece.