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.
Belgium said it had been unable to clear the way to approve an EU-Canada trade deal because a single region remains opposed.
"I have officially told Tusk that we have no agreement," said Belgium's Prime Minister Charles Michel after a meeting with regional leaders in Wallonia.
The Wallonians' implacable opposition threatens to derail the CETA trade agreement, which was seven years in the making.
Canada said it was "impossible" to continue talks last week, while the EU had given Belgium until Monday to hold crisis talks in the hope of reaching a compromise.
Michel said he was still open to dialogue with leaders in Wallonia, and that it was too early to say whether CETA was dead.
The breakdown of the talks has also highlighted the challenges faced by Theresa May as she attempt's to strike her own deal with the EU after the vote for Brexit.
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.