The change could be made within the next two weeks, Bloomberg quoted a source as saying.
Twitter has not yet commented on the report.
Back in January, founder Jack Dorsey said Twitter would explore ways of enabling its users to write longer posts.
Links currently take up to 23 characters of a tweet, reducing the space available to users for their own writing when sharing other online content.
The 140-character limit was originally added to make tweets fit into a text message. When the company launched in 2006, before smartphones were available, many users typed their tweets as texts before posting them.
Jack Dorsey has since described the limit as a “beautiful constraint” that “inspires creativity and brevity”.
However, Twitter has struggled to attract new users and has seen its share price decline by more than 70% in 2015.
In June 2015, Twitter announced it would increase the limit on direct messages between one user and another to 10,000 characters.
In January 2016, China’s biggest microblogging service, Sina Weibo, dropped its 140-character limit, allowing some users to write longer posts.
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