Twitter flags Trump tweet for premature claims of victory in South Carolina

Twitter has pinned a warning on a Trump campaign tweet declaring victory in the battleground state of South Carolina, saying it was premature and not confirmed by official sources.

A message under the tweet, in which the campaign trumpeted that Trump had won the Southern state, said official sources may not have called the race when this was Tweeted," the Politico reported.

The action came even as multiple news outlets - including The New York Times, The Washington Post, CNN and POLITICO - have similarly projected that President Trump will win the state, the report said.

The tweet, said the social media giant, violates a rule rolled out for this election that requires such tweets to be backed by calls from at least two of seven specified news organisations.

Twitter, though, left alone a similar Trump campaign tweet declaring victory in Florida because, the company said, it included a nod to one of Twitter's seven approved race callers.

In a seeming acknowledgment of Twitter's rules there, the campaign appended to its Florida victory tweet a note reading, Source:@DecisionDeskHQ.

The US' biggest social media companies have in recent days said that so-called premature declarations of victory were one of their primary concerns headed into this fraught Election Day, especially on a night expected to be full of close contests across the country.

A final verdict on who wins the presidency could take days or weeks depending on how the vote-counting, recounts and assorted court battles play out.