A top U.S. trade official said it would be "very difficult" for South Korea to join the ongoing Trans-Pacific Partnership (TPP) negotiations, which are on the verge of a deal.

"We think we are in the end game ... I think it will be very, very difficult for any country, including (South) Korea, to join the ongoing negotiations if you just look at the timetable and the clock," Acting Deputy U.S. Trade Representative Wendy Cutler said at a forum here.

After months of taking a wait-and-see stance, the South Korean government announced in late November that it would explore the possibility of joining TPP.

South Korea has focused on implementing its free trade agreement with the U.S., while the Obama administration has been negotiating with its 11 partners in the TPP talks. A deal is expected early next year.

Cutler described South Korea as a natural candidate for TPP and said its addition would add to the "political and strategic weight" of TPP.

She said Washington's consultations with potential TPP partners are typically two tracked -- focusing on their readiness to live up to the high standards of TPP and addressing bilateral issues of concern.

Cutler stressed the urgency of addressing some pending issues in implementing the South Korea-U.S. free trade agreement, called "KORUS FTA."  In March, it would mark the second anniversary of the pact taking effect.

Cutler, who led Washington's lengthy talks with Seoul on the FTA, cited four main sectors: customs origin verification, financial data transfer, automobile trade and organic goods certification systems.

Her remarks came amid growing concerns in South Korea that the U.S. may ratchet up trade pressure on Seoul by linking the implementation of the KORUS FTA with TPP.

Attending the forum, hosted by the Center for Strategic and International Studies (CSIS), South Korean Ambassador to the U.S.

Ahn Ho-young also said Seoul remains strongly committed to fully implementing the FTA.

It provides a firm base for South Korea to continue deepening economic relations with the U.S., he said.

Ahn added his country with a leading Asian economy is a "hybrid candidate" for TPP.

"Korea has been a very firm believer in the benefits of trade liberalization ... I am pretty sure that we can be a very meaningful participant in the TPP negotiations as well," he said.

Responding to criticism that South Korea was late to express its interest in TPP, meanwhile, a South Korean Embassy official here admitted that it would be hard for South Korea to enter the current phase of TPP talks on setting a broad framework of rules.

"We plan to concentrate efforts on holding bilateral talks on product trade among TPP members, which are of more significance in our domestic market than the negotiations on setting rules," the official said.

The TPP talks include a total of 12 nations - the U.S., Japan, Australia, Brunei, Canada, Chile, Malaysia, Mexico, New Zealand, Peru, Singapore and Vietnam.

The U.S. said China could be a candidate for TPP negotiations.

"China's been much more interested in TPP. We have launched talks with them under which we are updating them on TPP," Cutler said. (Yonhap News)