BEIJING - An official with the headquarters of China's Confucius Institute on Thursday said a US government directive asking the institute's Chinese teachers on American campuses to leave may harm the Sino-US friendship.

The official, who preferred to remain anonymous, said the headquarters regrets the US directive, and all of its centers around the world, including those on American campuses, were voluntarily requested by foreign partners, approved by the headquarters and jointly operated with Chinese colleges.

The Chinese teachers dispatched by the headquarters to the institutes were carefully selected and trained by both sides in an effort to help American elementary and secondary school students learn Mandarin and understand Chinese culture, the official said.

The directive sent by the US Department of State on May 17 to universities which sponsor Confucius Institutes states that any academics at university-based institutes who are teaching at the elementary- and secondary-school levels are violating the terms of their visas and must leave at the end of the current school term in June.

It said that after a preliminary review, the State Department has determined that the institutes must obtain American accreditation in order to continue to accept foreign scholars and professors as teachers.

A report by the US Chronicle of Higher Education said it is unclear what prompted the State Department to issue such a policy statement, as Confucius Institutes have been on American campuses for nearly a decade.

"If the teaching activities of the university-based Confucius Institutes were to be curtailed, that could have implications for US-China relations," the report said.

Confucius Institutes around the world are non-profit public institutions jointly established by the Confucius Institute Headquarters, or Hanban, and Chinese colleges and high schools with foreign educational institutions. The institution aims to teach the Chinese language and promote cultural exchanges overseas.

One of the institutes' most important missions is providing those studying Chinese in foreign countries and regions with standardized, authoritative and modern Chinese textbooks and learning opportunities, according to an introduction to the institutes.

Confucius Institutes have been opened in more than 350 educational institutions in 106 countries, and the amount of Confucius Classrooms in  elementary and secondary schools have increased to more than 500.

The United States currently has the largest amount of Confucius Institutes and Confucius Classrooms around the world, with 81 institutes and 299 classrooms in 48 states.

American universities such as Stanford University, Columbia University and the University of Chicago have sponsored the institutes and classrooms on their campuses with nearly 160,000 registered learners.

After the US State Department sent the directive, the College of William and Mary in Virginia replied with a letter, which said, "as the home of the newest Confucius Institute in the country, formally opened just a month ago, William and Mary has already witnessed firsthand the dramatic and highly positive impact of this program on our teaching, research, and community outreach about Chinese language and culture."

"Some aspects of the State Department directive, however, might severely restrict our efforts in these regards. Requiring the William and Mary Confucius Institute to gain independent accreditation, for example, would almost certainly force us to close our Confucius Institute," said the letter.

It added that the college hopes the State Department will work together with its Chinese partners to "support the efforts of Hanban, the agency that funds Confucius Institutes worldwide."

Gaston Caperton, president of the US College Board, said in April in Washington that China has played an increasingly important role in the international community and the American people, especially the young generation, need to know about China's economy, culture and folk customs.

Cultural exchanges are an important method of promoting mutual trust, and learning Chinese language is a bridge for achieving those objectives, Caperton said.

"Those Chinese teachers went to the United States with friendliness toward the American people, but they might return feeling the hurt, which is a kind of harm to the friendship between the American and Chinese people," said the Chinese official.