Twitter and TikTok's owner, ByteDance Ltd, have held preliminary talks about a possible merger that would involve the Chinese app's US operations, The Wall Street Journal reported, citing informed sources.

According to the newspaper, Twitter, however, is an unlikely bidder, as it is much smaller than Microsoft, which has been in talks with TikTok for weeks and has more resources to finance the deal.

TikTok's US operations are estimated at tens of billions of dollars, and Twitter would reportedly face difficulties paying for such a deal. Microsoft is thus seen as a front-runner in the bidding.

In addition, if the deal is secured, it will reshape the US social network, which focuses on short text messages, rather than videos, the newspaper noted.

Last week, President Donald Trump set September 15 as the deadline for TikTok to sell its US operations to Microsoft or another American company. Otherwise, the video-sharing app will be banned in the country on national security grounds.