"I am under no illusions," said European Commission head Jean-Claude Juncker as he arrived for the second day of the talks when asked on his hopes for a smoother 2016.
This year was also marked by deadly attacks by Islamists in Paris but also in Copenhagen, with the threat by violent and often homegrown extremists affecting all of Europe.
"I have never lived such a year that starts with terror and finishes with terror, that is marked by fear and deep crises," said European Parliament head Martin Schulz after the first day of talks.
The jihadist violence began in January with the shocking assault by French nationals against satirical newspaper Charlie Hebdo in Paris, followed by another assault in Copenhagen only a few week later, and then the November attacks in the French capital in which 130 people were killed.
The 28 leaders on Friday were to discuss ways to better pitch the battle against Islamic State jihadists after the massacres.
In a draft of the summit conclusions seen by AFP, leaders vowed to press on with a series of proposals made in February that have since remained stuck in the EU`s legislative pipeline.
These measures, which include a controversial plan to track airline passenger names in close coordination with the United States, "need to be urgently implemented", the statement said.
European authorities have grappled with revelations that several of the extremists behind the attacks were already known to police and had travelled freely across Europe in the months before their assaults.
`Good progress`
On Thursday British Prime Minister David Cameron laid out his plans at a summit dinner on how he intended to keep Britain in the EU in return for a difficult reform deal with his European partners.
He appealed to them to work with him on his demands including a freeze on benefits for EU migrants, before he holds a referendum on a possible "Brexit" by the end of 2017.
"Really good progress has been made but it is going to be tough," Cameron told a news conference.
EU President Donald Tusk said the other 27 leaders agreed to work for a compromise despite reservations and would finish the talks at a summit in February.
Germany`s powerful Chancellor Angela Merkel held open the possibility that the EU`s founding treaties could be changed at a later date to accommodate Conservative leader Cameron`s demands.
But France`s President Francois Hollande said he was opposed to treaty change.
The British dilemma stole the limelight from fresh efforts to tackle the migration crisis that has made this year one of the toughest in the bloc`s history and triggered many of the record 12 summits the leaders have held since January.
Europe has been deeply split in a year that has seen a record inflow of nearly one million refugees, crises in Greece and Ukraine as well as terror attacks in Paris.
Tusk said on Thursday leaders agreed to push through by June 2016 a plan for a new border and coastguard force that could intervene in member countries -- even without their consent -- in order to shore up the EU external frontier.
He said they also agreed to protect the Schengen area. The cherished European passport-free zone symbolises the ideal of free movement, but it has been threatened by the huge movements of people across the continent.
Wide rifts emerged over the migrant crisis after Merkel opened Germany`s doors to Syrian refugees, causing huge strains on transit countries and prompting several to suspend the Schengen rules and reintroduce border checks.
Key plans to solve the crisis have been bogged down, with a deal for member states to take in 160,000 refugees from overburdened Greece and Italy resulting in just 208 people being relocated so far.
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