WASHINGTON, Nov 18 (Reuters) - China on Friday pushed back on claims it was operating 'police stations' on U.S. soil, calling the sites volunteer-run, after the FBI director said he was "very concerned" about unauthorized stations that have been linked to Beijing's influence operations.Safeguard Defenders, a Europe-based human rights organization, published a report in September revealing the presence of dozens of Chinese police "service stations" in major cities around the world, including New York.China's Embassy in Washington acknowledged the existence of volunteer-run sites in the United States, but said they were not "police stations" or "police service centers."Republicans in the U.S. Congress, including Representative Jim Banks, have requested answers from the Biden administration about the operations of the sites.Rights activists say the sites are an extension of Beijing's efforts to pressure some Chinese nationals or their relatives abroad to return to China to face criminal charges, and have tied them to activities of China's United Front Work Department, a Chinese Communist Party body charged with spreading its influence and propaganda overseas."