"Some users were unable to sign in to Twitter. This issue was due to a bug in our front end code, which has been patched," the California-based company posted from the US West Coast late Sunday.
"We apologize for any inconvenience," Twitter said of the irregularities, which occurred from 4:00 pm to 9:25 pm in the California time zone (0000 GMT to 0525 GMT Monday).
"Something is technically wrong," the microblogging service's welcome page had said during the blockage. "Thanks for noticing-we're going to fix it up and have things back to normal soon."
Twitter claimed 284 million active users at the end of September.