BORACAY, Philippines (Reuters) - The United States is optimistic a deal to set up a free trade zone across the Pacific will be concluded soon, with sensitive issues likely to be ironed out when its Congress resumes sessions, the top U.S. trade official said on Sunday.

"We are very much in the end-game," U.S. Trade Representative Michael Froman told reporters after a two-day trade ministers' meeting on the Philippine island of Boracay.

"Our negotiators are working as we speak, and working through issues, we hope to conclude it soon," Froman said. "We want to make sure we conclude it consistent with the principles we've laid out."

The 12-nation Trans-Pacific Partnership (TPP), which will cover about 40 percent of the world's economies, took a major step forward on Friday when the U.S. Senate agreed to give President Barack Obama powers to speed up U.S. approval of trade deals.

The TPP, which will include economies from Japan to Chile, is part of Obama's so-called pivot to Asia, a strategy to counter China's rising economic and diplomatic influence.

After the U.S. Senate vote, the battle shifts to the U.S. House of Representatives where opposition is deeper to "fast-track" legislation granting the president powers to negotiate trade deals that Congress can approve or reject but not amend.

A divisive issue in the U.S. Congress centred on a proposed amendment involving sanctions on currency manipulation by trading partners. The Senate rejected that amendment, which opponents said would violate international trade rules and sink the pact.

"There are many issues that are likely to be discussed. Currency manipulation is an issue that is very important and ... we take very seriously," Froman said on debates in the House of Representatives, adding the United States was working on mechanisms to address the issue via the G-7, G-20 and the International Monetary Fund.

Froman declined to give a timeline on when the TPP talks would be concluded. But Australia said on Wednesday the negotiations could be wrapped up as early as June.

The U.S. Congress resumes sessions on June 1 after a 10-day Memorial Day holiday recess.

Japan is one of the TPP countries which prefer to wait for the United States to pass the fast-track legislation before concluding negotiations.

Chief negotiators from the 12 TPP countries are holding meetings in Guam that will run through to May 28 to try and bridge gaps for a deal on what would be the biggest trade pact since the North American Free Trade Agreement freed up trade between the United States, Canada and Mexico.

(Reporting by Rosemarie Francisco)