SHANGHAI, June 2 (Reuters) - Twitter Inc has apologised for suspending accounts critical of Chinese government policy days ahead of the 30th anniversary of a bloody crackdown on protesters at Beijing's Tiananmen Square, after an outcry among users.

In a statement posted to the company's Public Policy Twitter feed on Saturday, Twitter said "a number of accounts" had been suspended as part of efforts to target accounts engaging in "platform manipulation".

"Some of these were involved in commentary about China. These accounts were not mass reported by the Chinese authorities - this was a routine action on our part," the company said.

Such actions sometimes "catch false positives or we make errors," it added. Twitter said it was working to "ensure we overturn any errors".

Twitter's statement follows a sharp reaction from its users over the suspensions, including U.S. Senator Marco Rubio, who in a tweet accused Twitter of becoming "a Chinese (government) censor".

The approach of the 30th anniversary of the bloody June 4 crackdown on pro-democracy protests at Tiananmen Square has been accompanied in China by a tightening of censorship. Tools to detect and block content related to the 1989 crackdown have reached unprecedented levels of accuracy. (Reporting by Andrew Galbraith; Editing by Himani Sarkar)