Twitter mistakenly reset too many passwords on Thursday in response to a security incident, the company has said.

Twitter reset the passwords, and sent out letters informing people of the action, to a larger number of account holders than was necessary, the company said in a status update post.

"In this case, we unintentionally reset passwords of a larger number of accounts, beyond those that we believed to have been compromised," Twitter said. "We apologise for any inconvenience or confusion this may have caused."

An unknown number of user accounts may have been compromised "by a website or service not associated with Twitter," the company said in its letter.