Oct 7 (Reuters) - The United States is looking at restrictions on China’s Ant Group as well as Tencent Holdings Ltd over concerns that their digital payment platforms threaten national security, Bloomberg News reported on Wednesday, citing people familiar with the matter. Talks over how and whether to restrict Ant Group and Tencent’s payment systems has picked up pace among senior U.S. officials in recent weeks though a final decision isn’t imminent, according to the report. Ant Group, backed by Chinese e-commerce giant Alibaba , plans to list simultaneously in Hong Kong and on Shanghai’s STAR Market this month in what could be the world’s largest initial public offering, surpassing oil giant Saudi Aramco’s $29.4 billion float in December. Tencent Holdings and Ant Group did not immediately respond for comment out of regular business hours. (Reporting by Noor Zainab Hussain in Bengaluru; Editing by Maju Samuel)