The European Union gave Belgium until a leaders' summit on Friday to approve a troubled free trade pact with Canada which has been blocked by its small French-speaking region of Wallonia.

EU Trade Commissioner Cecilia Malmstroem said a planned visit by Canadian Prime Minister Justin Trudeau to sign the deal next week would not go ahead unless the federal Belgian government is able to endorse it.

"Yes there has to be an agreement. Our Canadian friends need to know whether they should book their ticket or not," Malmstroem said, when asked after EU trade ministers met in Luxembourg whether Friday's summit was the deadline.

"There are lots of things to discuss with our Canadian friends but if we don't manage to have this trade agreement there will not be (a visit by Trudeau) at this occasion," she said.

The parliament of the region of Wallonia last week voted to block the deal, known as CETA -- meaning that Belgium cannot sign up to the pact and leaving the deal in limbo after seven years of negotiations.

Slovak Trade Minister Peter Ziga, whose country holds the rotating presidency of the EU, said he was "optimistic" that Belgium and the EU would find a way to overcome the reservations expressed by Wallonia.

"Quite frankly I can't really imagine that the final stumbling block would be Belgium and I do believe pragmatism will open the way to an agreement," Ziga told a news conference with Malmstroem.

- 'High stakes' -

Wallonia's head of government Paul Magnette rejected the EU's ultimatum at a hastily organised commission hearing at the regional parliament after the EU talks.

"There are too many problems to be resolved to find a deal by Friday," Magnette said, according to Belga news agency.

Magnette said differences remained on thorny issues, including a contested investor protection system that has become a hot-button issue for the anti-CETA movement.

EU ministers fear that if CETA were to fail, it would send a signal to the world that it is difficult if not impossible to reach trade deals with Europe.

"Everyone is aware how high the stakes are for the EU," a senior EU official said ahead of the two-day leaders' summit in Brussels that starts Thursday.

"It's important that we are working to find a solution that is satisfactory for everyone including Wallonia, to put it bluntly," the official added.

The struggle to close the deal is also a worry for Britain, with many seeing CETA as a potential model for EU ties with the UK after Brexit.

"If we can't make it with Canada I'm not sure we can make it with UK," Malmstroem said.

Except for a few sensitive agricultural products, CETA abolishes virtually all tariffs between Canada and the EU.

Its backers say the deal will boost trade in goods and services between Europe and Canada by more than 20 percent, and total EU GDP by about 12 billion euros ($13.4 billion) per year.

But it is opposed by a wide array of groups, who say it is a test model to push through the even more controversial EU-US trade deal, still in negotiation.

- 'Out of touch' -

Belgium's pro-CETA Foreign Minister Didier Reynders said his EU counterparts "couldn't believe" the resistance by the Walloons.

"There is now an agreement of 27 countries, and we can practically say 27 and a half countries since the federal government and the Flemish government want to move forward," he said.

Belgium's complex political system includes parliaments for the regions of Flanders, Wallonia and Brussels, as well as legislatures for the Dutch, French and German-speaking communities.

The trade ministers' meeting was held as four activists from the international environmental group Greenpeace suspended themselves by rope in protest from the top of the conference centre where the talks were held.

Greenpeace sees the Canada deal as a Trojan horse for the far more ambitious free trade accord between the EU and US, known as TTIP. The group has campaigned against both CETA and TTIP, saying they threaten both environmental and consumer protection.

"The disagreements between ministers show how out of touch most of them are with their citizens," Greenpeace's trade policy adviser Shira Stanton said in a statement.