An unusual threat warning has been issued by the American, British, French, and Australian embassies in Beijing, warning Westerners to use extra vigilance when visiting the popular Sanlitun shopping district.

CNN describes the district as “home to a popular open-plan mall that boasts high-end brands like Mango, Reiss, and Lacoste, and some of Beijing’s best Western dining.”

A man used a sword to kill a Chinese woman and injure her French husband in the district in August, for no apparent reason. As the UK Guardian reports, the 25-year-old assailant calmly prowled through the shops with a samurai-style weapon before attacking the female victim outside a Japanese clothing store. He wounded her husband, then lingered at the scene, the whole crime captured on video. The attack appears to have been deranged violence, rather than terrorism, with little reason provided beyond the assailant’s alleged declaration that he “hated Americans.” He incorrectly believed his victim’s husband was one.

CNN reports Chinese police are aware of the new threat warning in the Sanlitun district. None of the embassies that issued the threat responded to CNN’s request for comment, possibly because their offices are closed for Christmas.

The L.A. Times reports that the authorities placed parts of Beijing on “lockdown,” filling the streets with “camouflage-clad guards toting large black rifles,” although Chinese police reportedly issued only a “yellow alert” through the Christmas weekend, which is the lowest rung of their three-level alert system. ABC News reported on Thursday afternoon that the security alert level for Beijing had been increased to “medium.”

Official statements have portrayed the increased police presence as a standard precaution for heavy holiday traffic, rather than the response to a terror threat.

Local residents, nevertheless, appear to believe something unusual is afoot, with the L.A. Times reporting heavy online chatter and intense search activity for the Sanlitun district.  Speculation is swirling that the new terror threat could have something to do with the restless Uighurs, a largely Muslim ethnic group in northwestern China.