LISBON, April 5 (Reuters) - A Portugal-based European consumer protection group has sued short-video app TikTok for allegedly allowing children aged under 13 to sign up for an account without parental consent and failing to implement measures to protect them. The lawsuit came a day after Britain's data watchdog said it had fined TikTok 12.7 million pounds ($15.81 million) for breaching data protection law, including by using the personal data of children without parental consent. Amid growing security concerns that China could use the Beijing-based company, owned by ByteDance Ltd, to harvest users' data, Australia, the United States, France and...