What Confucius Institutes do in the United States is visible through the work of those involved, and skeptics can visit the "open and transparent" branches for verification, said Gao Qing, head of the organization that supports 110 such institutes in the US.

Gao, executive director of the Confucius Institute US Center in Washington, spoke after what he said were attempts by some in the US capital to "politicize education matters", which he said will fail to derail operations of Confucius Institutes.

US Senator Marco Rubio warned in a Feb 5 letter of "the Chinese government's increasingly aggressive attempts to use Confucius Institutes and other means to influence foreign academic institutions and critical analysis of China's history and present policies".

Rubio, a Florida Republican, sent the open letter to a handful of Florida schools in which he said Confucius Institutes use the teaching of Chinese language and culture to expand political influence.

"The accusation is groundless and doesn't conform to the facts," Gao told China Daily, adding that the criticism coincides with strains in China-US relations in certain areas, since Washington designated Beijing as a rival.

Rubio, who chairs the Congressional-Executive Commission on China, urged the universities of North Florida, South Florida and West Florida, as well as Miami Dade College and Cypress Bay High School to terminate their Confucius Institute agreements.

Gao said Rubio's request had no impact on the University of West Florida, which decided last fall not to renew its institute agreement when it expires in May, citing a lack of student interest.

The University of South Florida, which in 2008 became the first Florida university to host a Confucius Institute, said it had found no evidence its institute had been compromised by the Chinese government.

Over the past decade, "we have not experienced any effort by the Hanban (the Confucius Institute headquarters in Beijing) to promote certain concepts or principles, and the nature of the partnership presented by our institution to the Hanban at each renewal has not changed," USF System President Judy Genshaft said in a reply letter to Rubio last week.

"The Confucius Institute at USF is in place to help our students and community develop a clearer understanding of Chinese language and culture, but academic authority for all content taught to students belongs exclusively to USF faculty," she said in the letter published in the Tampa Bay Times.

John Delaney, president of the University of North Florida, also said he saw no reason to discontinue classes offered by the institute, whose operation had prompted no complaints, The Florida Times-Union reported on Feb 7.

"The institutes' two Chinese instructors do not teach political science; they teach Chinese language, and without them, the university would offer fewer Chinese-language courses," the report quoted Delaney as saying.

Juan Mendieta, a spokesman for Miami Dade College, said it will provide a response "at an appropriate time". Cypress Bay High School, in Weston, had not responded.

"The Confucius Institute has expanded educational opportunities through language education and increased international exposure through cultural events, which are unavailable otherwise in Florida's underserved communities, especially in Miami," Gao said.

About 18 percent of the county's residents live below the poverty line, according to the latest US Census estimates.

Outside Florida, some US universities that run Confucius Institutes also said their programs are apolitical.

The CI at Western Kentucky University is not an academic unit, but a program supporting students of Chinese language and culture, meaning it doesn't engage in political or religious activities, said institute Director Weiping Pan.

Since its launch in 2010, the Confucius Institute at WKU has been positioned as a nonacademic unit; its faculty do not design the curriculum for the students, but teach the curriculum decided by professors of the Modern Languages Department, Pan told China Daily.