In a statement the UNESCO world heritage site, also known as the Palace Museum, confirmed that the incident happened on Monday, a day it is usually shut.

“The Palace Museum is deeply shocked and sincerely apologizes to the public,” it said late Friday on the Twitter-like platform Weibo, adding that it would “strictly manage and stop such actions” from taking place in future.

The controversial photos had been posted on Weibo this week but were swiftly deleted after sparking ire among users questioning how the women had entered the Forbidden City, which is very well guarded.