* Communist Party rattled by public discontent over graft
* Second spate of probes targets 10 provinces
* One of the provinces was base of ex-security chief (Recasts with senior official comments)
BEIJING, July 16 (Reuters) - China's anti-corruption chief pledged on Wednesday to broaden a crackdown on graft by focusing on officials with family abroad and including the province that was the power base of the former powerful head of domestic security.
The Communist Party leadership under President Xi Jinping has presided over the anti-graft campaign to shore up a ruling mandate shaken by suspicion that officials waste taxpayer money or use their positions for personal advantage.
Since his appointment last year, Xi has said that graft threatens the survival of the ruling party.
Wang Qishan, secretary of its watchdog Central Commission for Discipline Inspection, told investigators to go after "naked officials", state media said, referring to those who have children or spouses who live abroad.
Wang "urged inspectors to watch closely over corruption in mining, natural resources, land transfers, real estate development, construction projects, public and special funds," the official Xinhua news agency said.
Xinhua said a second round of inquiries in 10 provinces and regions will include Sichuan, where the former domestic security chief Zhou Yongkang, who is under virtual house arrest according to Reuters sources, once held the top party post.
At the peak of his influence, Zhou held one of the most powerful positions in China, overseeing the police force, civilian intelligence apparatus, paramilitary People's Armed Police, judges and prosecutors. The position, deemed too powerful, was downgraded after he retired.
Xi, who has pledged to go after powerful "tigers" as well as lowly "flies", has netted several senior figures in his corruption sweep, including Xu Caihou, former vice chairman of the Central Military Commission.
In the latest development, the party said on Wednesday that it had expelled two more former senior officials for corruption, paving the way for their prosecution.
The anti-corruption watchdog said in brief statements that Mao Xiaobing, former party boss of the western city of Xining, and Zhang Tianxin, former party chief of the southwestern city of Kunming, had "serious discipline problems".
"The investigation found that Mao Xiaobing took advantage of his post to seek profits for others, demanded and took a huge amount of bribes and committed adultery," the watchdog said in a statement. The former Kunming official, Zhang, had also abused his official position, with his dereliction of duty causing "a loss of state assets".
It was not possible to reach either of them for comment.
Communist Party members, especially senior officials, are supposed to be morally upstanding and adultery is considered a serious breach of party discipline.
State media also said that China would phase out official vehicles for uses other than for emergencies or law enforcement by the end of next year.
Last year, the military began replacing licence plates on its cars and trucks to crack down on legions of vehicles, many of them plush luxury brands, which routinely break traffic laws and fill up with free petrol.
"In China, officials above a certain level have usually been provided a driver and car for their work, but many have used the vehicles for private purposes, causing massive waste of public funds and widespread complaints," Xinhua said in a report.
The government will instead provide appropriate subsidies for civil servants to let them choose their own transport, it added. But this is unlikely to affect the sleek cars which carry Xi and his cabinet members about Beijing, as the rules make provision for "special services", likely to apply to the most senior officials.