BRASILIA/NEW YORK, Sept 21 (Reuters) - The United States will expand a quota for Brazilian sugar to be imported at a lower tax rate by 80,000 tonnes, in exchange for South America's largest country opening to more U.S. ethanol, Brazil's President Jair Bolsonaro said on Monday.

Bolsonaro's post on Twitter comes after Brazil on Sept. 11 said it would extend a tariff-free quota for U.S. ethanol by three months.

"The U.S. Trade Representative (USTR) said today ... that Brazil would receive an additional quota of 80,000 tonnes of sugar in the American market," Bolsonaro said.

"It is the first result of recently opened Brazil-U.S. talks regarding the sugar and ethanol sectors," he added.

The post said the quota would increase to 310,000 tonnes from 230,000 tonnes previously.

The Office of the U.S. Trade Representative did not respond to a request for comment.

Reuters had access to the text of the decision, which is expected to be published Tuesday in the U.S. Federal Register.

Besides Brazil, the USTR allocated an additional volume of 10,718 tonnes of raw sugar to Australia.

U.S. President Donald Trump has been trying to please corn and ethanol producers, a politically sensitive group which was hardly hit by the coronavirus pandemic.

Besides the talks with Brazil that resulted in the renewal of the tax-free quota for U.S. ethanol, the administration rejected requests from U.S. oil refiners for waivers that would have spared them from their obligation to blend biofuels like ethanol into their fuel. (Reporting by Lisandra Paraguassu in Brasilia and Marcelo Teixeira in New York; writing by Jake Spring; Editing by Dan Grebler)