BRUSSELS -- Prime Minister Theresa May signalled Friday that Britain is paving the way for trade talks with other countries well before it leaves the European Union but sought to reassure partners that this would not undermine the bloc's trade aims.

Facing EU leaders for the first time since she came to power on the back of the June U.K. vote to leave the bloc, May said she wants a smooth and co-operative relationship with her partners as the country heads out the exit door, probably in 2019.

Her conciliatory tone was in sharp contrast to the sometimes bitter rhetoric sparked by Britain's departure -- the first time an EU member has ever left the bloc -- including threats of a "hard exit" that would see the country stranded outside Europe's massive single market if it seeks to restrict the entry of EU migrants.

"I've been clear that the U.K. is discussing our future trade relationship with third countries," May told reporters at the end of a two-day summit in Brussels. "This will not undermine the EU's trade agenda. It is not in competition with it."

May said she wants "a mature, co-operative relationship with our European partners." She called for "give and take" and a willingness to approach the thorny divorce proceedings "in a constructive spirit."

So far, her EU partners are standing firm. Several reaffirmed that the EU's four cherished freedoms -- the free movement of goods, capital, services and people -- are indivisible, and that the U.K. cannot pick the choicest morsels.

Friday's summit talks were overshadowed by a major negotiating logjam as the small French-speaking region of Wallonia refused to endorse a new trade pact with Canada, leaving the entire 28-nation EU -- the world's biggest trading bloc -- in limbo.

May gave support to the negotiating efforts, even though her country will soon be leaving, but said Britain will be seeking to develop an entirely new trade relationship with Europe; not one that resembles any other which the EU has with the outside world.

"We're not looking to replicate a model that somebody else has," she said.

But Belgium Prime Minister Charles Michel warned that the Canada impasse is not a good sign for Britain.

"Everybody - and I am saying it as well - thinks that if the EU doesn't succeed in finalizing this economic treaty with Canada, this could mean that the discussions with the U.K. will also be very complex," he said.

Ultimately, May acknowledged, Britain's EU partners would have to move on and plan their future as 27 alone, although she insisted that London will assume all the responsibilities and obligations of membership until the exit negotiations conclude. That would probably be around two years after the expected launch of the talks in the first quarter of 2017.

For both the EU and the U.K., May said, "it's about seizing the opportunities of Brexit."