(Adds government comment)

BEIJING, Jan 9 (Reuters) - China has punished 17 officials for lapses in connection with explosions and riots in the Xinjiang region in September, state media said, as the regional Communist Party boss said the fight against "terrorism" was getting "more intense".

Dozens of people were killed in Xinjiang in the violence which began when explosions killed six people. Riots followed the blasts and police shot dead 40 people, some of whom were trying to blow themselves up, state media said at the time.

It was one of several violent incidents that have rocked the region in recent years. The government has blamed the trouble on separatists from the Uighur ethnic minority, most of whom are Muslim, who it says want to form an independent country called East Turkestan.

It is difficult for foreign journalists to report in Xinjiang, making it almost impossible to reach an independent assessment of the security situation.

After an investigation into the Sept. 21 violence, Xinjiang's Communist Party committee gave 17 officials "party and government disciplinary" punishment for security and other lapses, the www.ts.cn news site, which is run by the committee, said late on Thursday.

Zhang Chunxian, Xinjiang's party secretary, said the security situation was "extremely grim".

"Xinjiang's anti-terrorism fight has entered a phase that is more complicated and more intense," Zhang said, according to a report published by the website on Thursday. "We must take the initiative to brandish the sword, take the offensive and comprehensively attack."

The government has blamed attacks in other parts of China, including Beijing, on Islamist militants from Xinjiang.

Human rights activists say repressive government policies in Xinjiang, including curbs on religion and culture, as well as economic and social problems have provoked unrest. The government dismisses that.

The New York-based Committee to Protect Journalists has said Chinese authorities have detained two brothers of a Uighur reporter living in the United States.

A fourth brother was sentenced to five years in prison in 2014 for violating state security laws, the group said.

"We're deeply concerned by reports that family members of the Radio Free Asia journalist Shohret Hoshur continue to be harassed, including reports that his brothers have been imprisoned, apparently in retribution for his reporting," U.S. State Department spokeswoman Jen Psaki said on Thursday.

Chinese Foreign Ministry spokesman Hong Lei dismissed the criticism.

"I believe the relevant report is completely inconsistent with reality and not worth refuting," Hong told a Friday briefing. (Reporting by Michael Martina and Megha Rajagopalan; Editing by Michael Perry and Robert Birsel)