"They are engaged in conversation, they listen and hear us, but we are at this stage unable to determine the willingness factor," he told reporters on the sidelines of an event in Washington.

Beijing last summer imposed retaliatory tariffs of up to 70 percent on U.S. ethanol shipments, made exports to the key market uneconomical.

"We would certainly love below 15 percent," he said, referring to the tariff level. He did not say what the exact level U.S. negotiators were seeking.

Washington and Beijing have been locked in intense negotiations to end a trade war between the world's two largest economies that has cost both countries billions of dollars and roiled global financial markets.

Perdue on Monday said that a number of agricultural issues were on the table in trade talks, including poultry access, issues over beef exports, feed grains, ethanol and an animal feed known as distillers grains.

On Sunday, U.S. President Donald Trump said he would delay an increase in U.S. tariffs on $200 billion of Chinese goods and extend his March 1 deadline for a deal. It remains unclear how long the tariff increase would be delayed.

Washington wants Beijing to change the way it does business with the United States, demanding more access for U.S. companies, enforcement of intellectual property protection and an end to industrial subsidies.

Trump cited progress in the talks as the reason for not raising tariffs further on Chinese goods. He also sounded a note of caution, when he said a deal "could happen fairly soon, or it might not happen at all."

(Reporting by Humeyra Pamuk; Writing by Richard Valdmanis; Editing by Chizu Nomiyama and Susan Thomas)

By Humeyra Pamuk