This was not the first time that China has tried to block Isa from advocating for the Uighurs, a mainly Muslim ethnic group. He said he had been stopped before in New York, South Korea, Turkey and Switzerland.
The WUC has demanded the European Union investigate whether China pressured Italy into detaining Isa.
"The EU should be awakened and re-adjust its policies toward trade and political exchanges with China," said WUC spokesman Dilxat Rixat.
The EU hasn't responded to VOA's request for comment.
China's growing influence
Chinese Uighurs have long complained of discrimination and attempted assimilation by the dominant Han Chinese, and hundreds of people have been killed in Xinjiang during violence between the two groups. Uighurs describe the violence as a response to ethnic repression, but Beijing links it to Islamist terrorism elsewhere in Asia and has reacted with increasingly harsh measures.
"I used to say that China was practicing the carrot-and-stick approach to the Uighur problem," said Dru Gladney, a professor of anthropology from Pomona College in California. "But now it seems like the carrot is being completely removed and the stick is increasingly enlarged greatly."
Starting in September, the use of Uighur language will be banned at all school levels in Xinjiang. China also has barred Uighur parents from naming their newborns "Muhammad" or using other names that it says have "extremely religious" meanings.
"It is exactly the cultural genocide policy of the Chinese government toward the Uighurs," Isa told VOA.
"Uighur language is one of the main factors of Uighur identity. If you change your language, then, maybe 60 percent of identity would be lost. And another identity is religion. That's why the Chinese government today makes more pressure [on] religion and the language," he said.
Michael Clarke, an associate professor at Australian National University's National Security College, argued that China's intensified deployment of such controls will only heighten pre-existing anxieties among the Uighurs.
"There is no doubt that such policies exacerbate not only inter-ethnic tensions [i.e. between ordinary Uighurs and Han Chinese], but also Uighur relations with state institutions," the professor told VOA by email.
Professor Gladney of Pomona College called on the Chinese government to ease its heavy-handed controls in Xinjiang or face what he called "a speed bump" in its Belt and Road Initiative — an infrastructure project that passes through the far west region.
To execute the project, China needs popular support from countries in Central Asia or Arab states of the Persian Gulf, where Muslim populations are increasingly angry over China's treatment of Uighur Muslims, he said.