Chinese President, Xi Jinping attends a signing ceremony with President of the Federal Republic of Nigeria, Muhammadu Buhari (not pictured) at the Great Hall of the People in Beijing, April 12, 2016. REUTERS/Kenzaburo Fukuhara/Pool

BEIJING (Reuters) - China's ruling Communist Party is not trying to curtail internal debate or even criticism with rules banning "baseless comments" but is simply trying to ensure no one is "singing out of tune", President Xi Jinping has said.

Xi has come down hard on corruption since assuming office more than three years ago and tried to return the party to its traditional values of serving the people selflessly, following a series of graft and extravagance scandals.

Along with his fight against corruption, Xi has also been reining in overt dissent by party members on key issues as he seeks to enforce party discipline, especially on tackling graft, with new party rules unveiled last year banning "baseless comments" on major policies.

In a January speech, the full transcript of which was carried by the party's official People's Daily on Tuesday, Xi said some party members had been feigning compliance with policy and even openly expressing opposition.

"Some party organizations think political discipline is soft or false, and when it comes to wrong words and deeds that go against party discipline they don't care, don't report it, don't resist it, don't fight it and certainly don't investigate and deal with it," Xi told the party's anti-graft watchdog.

"The reason we demand party members and cadres not to make baseless comments is not so you can't raise opinions and suggestions or even critical opinions," he said.

"It's so that on important political principles, on issues of right and wrong (you) cannot sing out of tune with the party center and engage in political liberalism."

The party periodically warns against "liberalism", especially in the military, which generally refers to those who wish to challenge the extent of party control over China.

Speaking more generally about corruption, Xi said the fight against the problem remained "severe and complex".

Without naming individuals, he said some officials cared only about forming their own cliques to advance their careers - something the party has long railed against as a root cause of corruption.

There has been persistent speculation that the graft crackdown is as much about Xi taking down his rivals as it is about dealing with the actual problem itself. The party denies this.

(Reporting by Ben Blanchard; Editing by Paul Tait)