TEGUCIGALPA, Nov 22(Reuters) - The top two contenders to be the next president of Honduras held boisterous final rallies over the weekend, one week ahead of an election that could end diplomatic support for Taiwan in the Central American country if the leftist candidate wins. On Monday, a visiting U.S. diplomat called for "free, fair and transparent elections" following a meeting with Honduran electoral authority CNE, in a fresh sign of American interest in the Nov. 28 vote. Should poll leader Xiomara Castro, of the leftist opposition Libre Party, beat the ruling National Party"s Nasry Asfura and put an end to its dozen-year run in power, she would also become the first woman to be president in Honduras. "We"re going to take out the dictatorship," she thundered on Sunday, before thousands of supporters in downtown Tegucigalpa, in a nod to the bitterly disputed re-election of outgoing President Juan Orlando Hernandez in 2017. Castro is running on an anti-corruption platform, while also favoring a partial legalization of abortion and a diplomatic opening to China, which would mark a major shift from country"s current embrace of Taiwan over Beijing. "As a united opposition, we say enough to so much thieving, so much corruption and drug trafficking," said Castro, who has also pointed to the conviction of Hernandez"s younger brother on drug charges in the United States earlier this year. In a visible reminder of the united opposition backing her, Castro"s crowd was also peppered with the flags of the party of her running mate, television host Salvador Nasralla, the 2017 runner-up who describes his views as center-right. Brian Nichols, the U.S. assistant secretary of state for the Western Hemisphere, arrived in Honduras on Sunday and met with a local elections watchdog prior to holding talks with CNE officials on Monday, according to posts on social media. "I underscored U.S. support for free, fair, transparent and peaceful elections in Honduras," Nichols wrote on Twitter. Castro, 62, is the wife of former President Manuel Zelaya, who was deposed in a 2009 coup, after business and military leaders allied against him. Presidential hopeful Asfura, a 63-year-old two-term mayor of the capital, held his own final rally on Sunday at a baseball stadium, projecting confidence despite trailing in a recent poll. "We"re going to create jobs and opportunity," he said. "We"re going to work hard on social programs that bring progress and development to the entire country." Both candidates also held final rallies with supporters on Saturday in Honduras" second biggest city and industrial hub, San Pedro Sula. Unlike Castro, Asfura has not offered a detailed campaign platform. A poll earlier this month showed Castro with a 17 point lead, but some analysts still expect a tight race.