BEIJING — Five Chinese activists defied a security guard and made a brief visit to dissident Liu Xiaobo’s wife, Liu Xia, who has been confined under house arrest since her husband was awarded the Nobel Peace Prize two years ago.

The rare visit Friday was captured on video by Beijing activist Hu Jia, who posted it on YouTube on Monday. Hu said the activists wanted to see Liu Xia on that day to mark her husband’s birthday.