Prime Minister Theresa May has said Britain will play a "full and active role in the EU" until it leaves.
Following Brexit, Britain will remain "open" and "outward looking" and is committed to trading freely with other European countries, she said.
The prime minister is attending her first EU summit following the referendum.
The breakdown of talks intended to create a free trade zone between Canada and the EU has highlighted the challenge faced by Theresa May as she attempts to strike her own deal with the bloc after the vote for Brexit.
One small region of Belgium is blocking a planned CETA trade deal with Canada that was seven years in the making - and it will have a similar power of veto over any agreement with Britain.
If the UK votes for a hard Brexit then it will need to have inked an agreement with the bloc within just two years - but European leaders are already warning that could be virtually impossible.
"If there are all these problems to have a simple trade agreement with Canda, just imagine a trade agreement with the United Kingdom," said Malta's president Joe Muscat.
Asked if she was undermining the UK position, she said: "You can't undermine something that doesn't exist."
The deal would set up a free trade zone between the EU and Canada - and could be an important test for the UK's Brexit negotiations.
European Commission President said an EU-Canada free trade deal would help end Canadian visa restrictions for Romanians and Bulgarians.