A new WeChat feature showing a cascade of US flags, apparently commemorating Martin Luther King Day in the United States, has provoked the ire of Communist Party authorities. Chinese mobile users were surprised to see icons of the Star-Spangled Banner "rain down" their app screen whenever they typed the words “civil rights” in conversations with friends. WeChat, developed and operated by internet giant Tencent, apologised on Monday, saying the feature was only supposed to be available to US users, but technical errors resulted in it being available to Chinese users. "Due to some backstage setting errors, it has been available to all WeChat users," it said this afternoon. "We apologise for any misunderstandings caused." The new feature only appeared in the past few days, seemingly to mark the birthday of King, an African-American civil rights activist and Nobel laureate who espoused civil disobedience and led protests against racial discrimination in America. Martin Luther King Day is a US federal holiday celebrated on the third Monday of January each year. On social media, Chinese officials earlier slammed the add-on as inappropriate for WeChat to roll out a feature for a US public holiday and not "patriotic" Chinese ones. “[We] also tried keywords like ‘National Day’, ‘China’, and ‘Five-Starred Red Flag’ [the national flag of China], but nothing happens!” the Committee of the Communist Youth League in southern Fujian province said in a Weibo post . “What are your intentions?” the league said, questioning WeChat’s decision. The league is chiefly responsible for cultivating elite Chinese youth who aspire to become fully-fledged members of the party. Joining the youth league is considered crucial to joining the party itself. The "flying emoticons" feature has been available to millions of WeChat users worldwide for some time, which recognises keywords such as "Happy Birthday" or "Christmas" in people's chat messages and fills the chat screen with emoticons fitting the occasion or mood. "Keywords that trigger falling emoticons can also be specific to your country and the unique occasions you celebrate," said WeChat on its official English-language blog in a November 2014 post . As of Monday afternoon, the league’s comment on Weibo has been reposted more than 6,500 times and elicited some 2,600 comments from users. Several of the league’s supporters accused WeChat of “pandering to the United States”. Others were nonplussed, saying communist authorities were overreacting. “What’s so important about this? Why does everything have to be politicised?” a user said on Weibo. After the debate erupted over the weekend, some users reported the feature had been taken down as of Monday morning – but many others said it was still working.