I wouldn't normally quote Wikipedia at length but …

“Other estimates

Unofficial estimates of the death toll have usually been higher than government figures, and go as high as 10,454.[2] Nicholas D. Kristof, then Beijing bureau chief for The New York Times wrote on June 21 that "it seems plausible that about a dozen soldiers and policemen were killed, along with 400 to 800 civilians."[1] US ambassador James Lilley said that, based on visits to hospitals around Beijing, a minimum of several hundred had been killed.[157] In a 1990 article addressing the question, Time magazine said that the Chinese Red Cross had given a figure of 2,600 deaths on the morning of June 4, though later this figure was retracted.[158] A declassified NSA cable filed on the same day estimated 180–500 deaths up to the morning of June 4.[159] Amnesty International's estimates puts the number of deaths at between several hundred and close to 1,000,[158][160] while a Western diplomat who compiled estimates put the number at 300 to 1,000.[1] Official US Government papers declassified in 2014 estimated there had been 10,454 deaths and 40,000 injured. In British Government papers declassified and made public in December 2017, it was revealed that its ambassador to China, Alan Ewen Donald had reported in 1989 that a member of the State Council of the People's Republic of China had estimated the civilian death toll at 10,000.[2][161]”

“Identifying the dead

The Tiananmen Mothers, a victims' advocacy group co-founded by Ding Zilin and Zhang Xianling, whose children were killed during the crackdown, have identified 202 victims as of August 2011. The group has worked painstakingly, in the face of government interference, to locate victims' families and collect information about the victims. Their tally has grown from 155 in 1999 to 202 in 2011. The list includes four individuals who committed suicide on or after June 4, for reasons that related to their involvement in the demonstrations.[162][163]

Wu Renhua of the Chinese Alliance for Democracy, an overseas group agitating for democratic reform in China, said that he was only able to verify and identify 15 military deaths. Wu asserts that if deaths from events unrelated to demonstrators were removed from the count, only seven deaths among military personnel may be counted as those "killed in action" by rioters.[109]”

https://en.wikipedia.org/wiki/Tiananmen_Square_protests_of_1...

Clearly the figures are contested and undoubtedly 10s of security personnel were killed by protestors and hundreds (at least) of protestors were killed by security personnel. There's a _big_ jump between various claims of ‘in the hundreds’ and the ~10,000 claims made by US and UK declassified government papers. One would expect some sort of evidence eventually to filter out to support a figure as high as that, not “his source was someone who "was passing on information given him by a close friend who is currently a member of the State Council".” – that's not evidence, that's hearsay. I'm not saying the figure couldn't be that high, I'm saying extraordinary claims need more substantial backing up.

edit: Just to be clear – hundreds killed protesting political reform is in itself absolutely shocking when you think about it.