The European Union is in a “critical situation”, the German chancellor has said, as leaders meet in Slovakia to discuss ways to regain trust after the UK’s vote to leave the bloc.
Angela Merkel said they needed to show they could improve on security, defence co-operation and the economy.
But EU countries are deeply divided over how to bolster growth and respond to the influx of migrants.
Meeting in Bratislava without the UK, they will not discuss Brexit talks.
“We need solutions for Europe and we are in a critical situation,” Mrs Merkel said as she arrived at the gathering.
“You can’t solve all Europe’s problems in one summit. What we have to do is show in our deeds we can do things better in the realms of security and fighting terrorism, and in the field of defence.”
Even though Britain’s referendum result is not on the agenda, and British Prime Minister Theresa May is not attending the summit, there is little doubt that Brexit will overshadow the meeting.
The Lithuanian President, Dalia Grybauskaite, said the bloc was facing “huge external challenges” and Brexit was one of them.
Heavy on symbolism, light on results: By Katya Adler, BBC News, Slovakia
Donald Tusk is hoping for a public show of unity among the 27 nations of the EU following Britain’s vote to leave in June.
Mr Tusk wants to restore EU stability and credibility with the bloc in the face of a migrant crisis and issues with the euro currency. But European leaders are divided, their voters sceptical.
Central and Eastern Europe want powers back from Brussels. Northern nations view the south as a eurozone liability. Mediterranean countries balk at German austerity edicts.
So on Friday they will stick to subjects they agree on and those they feel are relevant to voters’ concerns: migration, security and globalisation.
The hard stuff, such as a future trade deal with Britain and how to save the single currency, will be left for another day.
Earlier, Donald Tusk, the European Council President, called on EU leaders to assure citizens they had learned lessons from Brexit and were able to “bring back stability and a sense of security”.
He urged them to take a “sober and brutally honest” look at the bloc’s problems.
The EU response to the influx of migrants is one of the most contentious points among members.
The summit host, Slovak Prime Minister Robert Fico, is one of a group of central and eastern European leaders who object to the EU quota system which distributes migrants across the EU.
He has said Slovakia will not accept “one single Muslim migrant” and has mounted a legal challenge to the scheme.
Slovak Prime Minister Robert Fico (right, with Mr Tusk) has made it clear his country does not want to take a share of the migrants coming to Europe
On Tuesday, Luxembourg’s Foreign Minister Jean Asselborncalled for Hungary to be suspendedor even expelled from the EU because of its “massive violation” of fundamental values, specifically the government’s treatment of refugees.
For France, the priority is border security in the wake of a number of Islamic extremist attacks in the country.
France and Germany have outlined plans to deepen European military co-operation, which were reinforced in the State of the Union address by European Commission President Jean-Claude Juncker on Wednesday, in which he called for a European military headquarters.
The UK’s departure from the EU removes one of the biggest obstacles to stronger EU defence in tandem with Nato.