Twitter has suspended a number of fake accounts which purported to be run by black supporters of US President Donald Trump.

They are thought to have attracted more than a quarter-of-a-million retweets or mentions on Twitter before they were suspended.

The accounts often used profile pictures taken from news reports and frequently used the wording 'Yes I'm black and I'm voting for Trump!'

The accounts sometimes claimed to be owned by military veterans or members of law enforcement.

Twitter said the accounts broke its rules on spam and platform manipulation.

"Our teams are working diligently to investigate this activity and will take action in line with the Twitter Rules if Tweets are found to be in violation," a spokeswoman for the social media company said.

Twitter's policy against platform manipulation and spam prohibits coordination among accounts to artificially influence conversation, including the use of multiple or fake accounts.

Twitter declined to specify the number of accounts suspended or to comment beyond its statement.

Darren Linvill, a social media disinformation researcher at Clemson University in South Carolina who said he had been tracking the accounts since Saturday, found more than two dozen accounts that collectively had 265,000 retweets or Twitter mentions.

He said the accounts ranged in size but some had attracted tens of thousands of followers.

Mr Linvill said some of the accounts used photos of Black American men that had appeared in news articles.

Some used identical images of Mr Trump as their header image.

Mr Linvill said all the accounts he had been tracking in the group had now been suspended by Twitter, but the damage had already been done.

"It doesn't matter if Twitter's shutting you down in four days, they've already had their impact," he said.