The top U.S. trade negotiator voiced optimism on Monday about a proposed free trade agreement with South Korea, saying that "important" progress has been made toward the goal.

"I remain encouraged and optimistic that we can do this under the TPA deadline," Wendy Cutler said, referring to U.S. President George Bush's "fast-track" trade promotion authority which expires on July 1.

Under Bush's authority, U.S. negotiators have until April 2 to submit a deal for a mandatory 90-day review by Congress before voting for or against a deal without amendments.

The deal also requires ratification by South Korea's parliament but the U.S. time restriction has raised concern over whether the agreement can be sealed in time.

Cutler, who also serves as deputy chief of the U.S. Trade Representative, said "important" progress made so far has convinced her to be optimistic about the deal.

She said, however, that "a lot of work" still has to be done.

Prior to this round of talks in Seoul which opened on Monday, the two countries decided not to officially discuss three key pending issues - anti-dumping rules, autos and medicine.

But Cutler said that that decision would have no impact on the the talks, explaining that they will be tackled at informal talks involving her and her South Korean counterpart, Kim Jong-hoon.

"The U.S. is prepared to make progress in all of these three issues at the chief negotiator level," Cutler told reporters after ending the morning session.

Cutler also demanded a full opening of South Korea's beef market, warning that the issue is "critical" in reaching a free trade deal with South Korea.

"We will figure out the speediest way, taking into consideration international standards in this area," she said, commenting on South Korea's strict quarantine rules that have virtually blocked U.S. beef imports.

Lifting a three-year ban prompted by the outbreak of mad cow case in the U.S., South Korea agreed to resume only boneless U.S. beef last fall.

It has since turned back three shipments totaling 22.3 tons after bone chips were found in the meat.

The beef issue is extremely sensitive for South Koreans, because scientists say mad cow disease can be transmitted to humans by bone marrow of cows infected with the disease.

Before the beef import ban was imposed in 2003, South Korea was the third largest U.S. beef market with annual purchases reaching US$850 million.