WASHINGTON - US senators expressed on Thursday concerns over the prospects of a Trans-Pacific Partnership (TPP) trade deal despite progress made last week between the United States and Japan.

Orrin Hatch, the top Republican at the Senate Finance Committee, said the administration's trade agenda was at risk of failure without trade promotion authority (TPA).

"I do not believe you can conclude high-standard agreements that will meet Congress' approval without TPA," he said during a hearing of the Senate Finance Committee. "History tells us very clearly that without TPA, your trade agenda will almost certainly fail."

TPA, known as "fast track" trade legislation, provides that Congress must vote up or down on a proposed trade agreement without the possibility of amendment. Without that guarantee, it's more difficult for other negotiating countries to make significant concessions.

"The political clock is ticking and it won't be long until we will lose the small window we have to pass significant trade legislation this year," Hatch noted.

Charles Schumer, a top senate Democrat in the committee, also warned that the TPP agreement wouldn't win congressional approval unless it included currency manipulation provisions in the trade deal.

"Strong language on currency manipulation is a vital first step to earning Democratic support to pass TPP in the Senate," he said.

Washington had hoped to complete TPP trade negotiations by the end of last year, but representatives from the 12 participating countries in the Asia Pacific failed to reach a deal in the past several months amid disagreements between the United States and Japan.

The two countries "crossed an important threshold in our bilateral market access discussions," US Trade Representative (USTR) Michael Froman said, referring to US President Barack Obama's visit to Tokyo last week.

"We've identified a path forward on agriculture and autos, two of the most challenging areas of our negotiations with Japan," said he said, adding that currency issues had not been discussed yet in current TPP negotiations, as the US Treasury Department has the lead on the issue.

Froman said this "milestone achievement" would provide "significant momentum" to the overall TPP negotiations, although work remains to close the gaps.

The administration was looking forward to working with the Senate Finance Committee (SFC) and Congress as a whole to secure TPA that has as broad bipartisan support as possible, he said.

But SFC Chairman Ron Wyden said that he was still talking to colleagues and there was no timetable for when such a bill might be ready.

Analysts said that it's unlikely for Congress to pass the TPA bill before midterm elections in November. Therefore, chances of wrapping up the TPP trade deal this year appear slim.

The TPP talks were initiated by Singapore, New Zealand, Chile and Brunei Darussalam in 2005, but dominated by the United States after it joined the talks in 2008. Japan joined the TPP talks last year.