Three Han Chinese officials were murdered in Xinjiang as President Xi Jinping visited the restive region, home to mainly-Muslim Uighurs, a report and online postings said.

The trio were killed late last month while on a fishing trip in Kargilik county in Kashgar prefecture, US-funded Radio Free Asia (RFA) said Wednesday, quoting local sources.

"Two of the men had their throats cut and were dumped into the lake, while the third one was stabbed in 31 places before he was also pushed into the lake," RFA quoted Enver Tursun, deputy chief of the police station in Janggilieski, as saying.

RFA's Chinese-language report attributed the quote to information received by its Uighur service.

Xinjiang, in China's far west, is periodically hit by unrest, which Chinese authorities blame on separatists from the area. Rights groups say tensions are driven mainly by cultural oppression, intrusive security measures, and immigration by Han, China's ethnic majority.

All three victims transferred to Xinjiang two years ago and were senior county level officials, one heading a bank and the other two working in the telecommunication department, RFA said.

Xi was in Kashgar on the same day -- the start of his four-day trip to the region -- visiting armed police units and stressing the "gravity and complexity" of anti-terrorism situation in the area, according to a previous report by the official Xinhua news agency.

On the last day of Xi's trip, assailants using knives and explosive devices struck at a rail station in Xinjiang's capital Urumqi, leaving three dead -- including two attackers -- and 79 wounded.

The Turkestan Islamic Party (TIP), a militant Islamist group, released a video online showing the construction of a briefcase bomb allegedly used in the attack, the US-based SITE Intelligence Group, which monitors extremist organisations, said Tuesday.

Asked about the video, foreign ministry spokeswoman Hua Chunying said it "once again confirms what China has said previously, that currently there are some extremist violent terrorist groups trying... to carry out violent terrorist incidents in Xinjiang and other parts of China".

But several analysts doubt whether TIP has the capability to launch such attacks, suggesting that it could be looking to raise its profile.

"The leader of TIP ... has claimed in the past responsibility for a number of other incidents which it seems that the TIP wouldn't actually be capable of doing," Michael Clarke, an expert on Xinjiang at the Griffith Asia Institute in Brisbane, Australia, told AFP.

- 'Government is weak and incapable' -

Authorities in Kashgar were not available for comment on the reported triple murder case when contacted by AFP on Thursday.

China's state-controlled media have remained silent on the incident, but an online statement allegedly signed by the three men's widows pleading for justice has been circulating on Internet forums.

The note, dated May 3, complained that authorities in Kargilik attempted to cover the incident up and pressured the relatives to bury the bodies "as soon as possible", according to a reposting on www.hanminzu.org, a US-registered Han nationalist website.

"The government is so weak and incapable... It cannot firmly fight the arrogance of the violent terrorists," said the note. "How can we dare to go out in the future?"

It did not mention the dead men's ethnicity or their official posts.

A user of China's Twitter-like Weibo, who often sends pictures of himself in Xinjiang, also posted earlier this month that a friend's uncle and two other people were killed by "thugs" on the afternoon of April 27. The posting, already deleted, can still be seen on freeweibo.com, a website that tracks censored Weibo posts.

Violent incidents have escalated beyond Xinjiang in recent months, with a horrific knife assault in March at a railway station in the southern city of Kunming, which left 29 dead and 143 wounded, dubbed the country's "9/11" by some Chinese media.