(Updates with quotes, details on meetings and background)

By Dave Graham

MEXICO CITY, April 30 (Reuters) - The 12 countries working toward a historic Pacific trade pact could reach a deal at the end of May, though Canada must still show greater willingness to open up its markets, a senior Chilean official said on Thursday.

Chile is among the nations in talks over the Trans-Pacific Partnership (TPP), a trade pact that would cover 40 percent of the world economy and includes the United States and Japan.

Andres Rebolledo, head of international economic relations for Chile, said a ministerial meeting had been set for May 26-28, and that a potential deal is in sight.

Boosting the prospects of an accord, was the fact that approval for fast-track legislation in the U.S. Congress needed to underpin the TPP appeared to be "imminent," Rebolledo said in an interview with Reuters in Mexico City.

The fast-track bill should help the TPP by persuading the United States' partners that the trade deal will not be picked apart in Congress later, officials say.

"This all suggests that probably towards the end of May there will be the closing round of negotiations," Rebolledo said, noting that there were still tough talks ahead.

The ministerial meeting would be held on the island of Guam, a U.S. territory in the western Pacific, another senior official involved in the TPP negotiations told Reuters.

Prior to that meeting there would be intensive "technical meetings" and bilateral talks to resolve outstanding differences, Rebolledo said, adding that agreeing on access to markets was still a bone of contention.

While progress had been made with Japan on this point, Canada needed to give ground, he said.

"(Canada's) offer is still the most limited," he added.

A further sticking point for Chile, Rebolledo noted, was the issue of intellectual property rights.

(Reporting by Dave Graham; Editing by Lisa Shumaker)