BEIJING, May 6, 2009 (AFP) - China said it had suspended expedited processing of visa applications by US citizens but declined comment on whether it was part of measures to prevent swine flu reaching Chinese shores.

The change was announced on the website of the Chinese embassy in Washington.

"The Chinese visa processing time will be changed to six business days while the express and rush service for visa applications will be suspended," the statement on the website said.

A foreign ministry spokesman on Tuesday declined to answer when asked whether the measure was linked to the (A)H1N1 virus and whether China was making similar changes for applicants from other countries.

China has instituted tough measures to try to prevent the spread of the virus onto its soil, including quarantining some foreign visitors.

This has led to charges from Mexico, the epicentre of the current outbreak, that China is discriminating against Mexican nationals.

But the Chinese embassy notice said that all visa applicants must fill out a form whose sole purpose is to establish which countries the applicant has visited over the past two weeks.

The current swine flu outbreak began in Mexico about two weeks ago.

A spokeswoman for the US embassy in Beijing told AFP that China had informed the United States of the change but said she was unaware of the reason.

After repeated denials, China last year acknowledged adopting more stringent visa requirements in the months preceding the Beijing Olympics in August, saying they were meant to ensure a "safe environment" for the Games.

China this year faces a number of sensitive anniversaries including 20 years since the June 4 crackdown on Tiananmen Square democracy protests, in which the army killed hundreds and possibly thousands of Chinese citizens.

China also celebrates the 60th anniversary of the founding of the People's Republic of China in October.