(Adds Twitter comment, detail about Trump claims)
SAN FRANCISCO, May 26 (Reuters) - Twitter on Tuesday for the first time prompted readers to check the facts in tweets sent by U.S. President Donald Trump, warning readers his claims about mail-in ballots were false and had been debunked by fact checkers.
The blue exclamation mark notification prompted readers to "get the facts about mail-in ballots" and directed them to a page with news articles and information from fact-checkers about the claims.
"Trump makes unsubstantiated claim that mail-in ballots will lead to voter fraud," a headline at the top of the page said.
Trump had claimed in tweets earlier in the day that mail-in ballots would be "substantially fraudulent" and result in a "rigged election." He also singled out the governor of California over the issue, although the state is not the only one to use mail-in ballots.
Twitter confirmed this was the first time it had applied a label to a tweet by the president under its new "misleading information" policy, introduced earlier in the month.
(Reporting by Katie Paul and Elizabeth Culliford; Editing by Leslie Adler and Howard Goller)
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