Twitter is in "advanced talks" to buy TweetDeck, a popular platform for accessing the service, for some $50 million, The Wall Street Journal reported on Monday.
Asked about the report, Twitter said: "We don't comment on rumours. We don't provide off-the-record background on rumours. We don't wink twice or release puffs of smoke about rumours."
While declining to comment on a TweetDeck acquisition, a Twitter spokesman did confirm that the San Francisco-based startup had plans to open an office in London, as reported by the Journal.
The spokesman said Twitter, however, had not yet determined where it would locate a European headquarters.
TweetDeck is one a number of programs used to access Twitter from mobile phones, laptops or desktop computers. TweetDeck employs around 15 people, most of whom are located in Britain.
The Journal's report of a TweetDeck acquisition comes amid management changes at Twitter.
Twitter co-founder Jack Dorsey returned to the company last month as executive chairman to head its product team.
Dorsey, who founded Twitter in March 2006 with Biz Stone and Evan Williams, resigned as Twitter's chief executive in 2008. He remained chairman of the company but did not take an active role in daily operations.
More than 200 million people use Twitter, firing off more than 140 million messages of 140 characters or less daily.