* Three dead, 79 injured in bomb and knife attack
* Happens as President Xi wrapping up Xinjiang tour
* Xi vows "decisive actions" against the "terrorists"
* Western region scene of growing unrest and violence (Recasts, updates throughout)
By Ben Blanchard
BEIJING, April 30 (Reuters) - Three people were killed and 79 wounded in a bomb and knife attack at a train station in the far western region of China on Wednesday, state media said, as President Xi Jinping was wrapping up a vist to the area.
Xi promised "decisive actions" against the "terrorists" behind the attack in Xinjiang, a region beset for years by violence the government blames on Islamist militants and separatists seeking an independent state called East Turkestan.
Quoting police, Xinhua news agency said "knife-wielding mobs slashed people" at an exit of the South Railway Station of Urumqi, capital of the Xinjiang region, and set off explosives.
Pictures on China's Twitter-like Weibo site showed blood on suitcases and debris on the ground in front of the station. Many posts carrying the images were later removed by censors.
Xinhua said the station re-opened at 9 p.m. (1300 GMT), around two hours after the attack, under heavy police presence. Four people were seriously wounded but were in stable condition.
It was not clear if President Xi was still in Xinjiang at the time of the attack, at the end of his four-day visit to the region during which he stressed tough policing to fight "terrorists".
Responding to the attack, he said: "The battle to combat violence and terrorism will not allow even a moment of slackness, and decisive actions must be taken to resolutely suppress the terrorists' rampant momentum," Xinhua reported.
Xi said the battle against separatists would be "long-term, complicated and acute".
Exiles and many rights groups say the cause of unrest in the resource-rich and strategically located region is heavy-handed conduct by authorities, including curbs on Islam and the culture and language of its Muslim Uighur people.
Dilxat Raxit, spokesman for the Germany-based World Uyghur Congress exile group, said he feared the incident would lead to a new round of repression against Xinjiang's Uighurs.
"It's extremely worrying. No matter what happens, China first of all represses the Uighurs, leading to many innocent Uighurs being locked up," he said by telephone.
"We can see from this that Xinjiang is in a period of turmoil, and such incidents could happen again at any time. This is the trend and it's directly related to Beijing's policies."
Unrest in Xinjiang has caused the deaths of more than 100 people in the past year, prompting a tougher stance against Turkic-language speaking Uighurs, many of whom resent government controls on their culture and religion.
Urumqi was the scene of deadly ethnic riots in 2009, with nearly 200 people killed when Uighurs clashed with members of the majority ethnic Han Chinese community. It has been relatively calm since.
Many Chinese took to the Weibo microblogging service to express anger and defiance at the station attack, including Hu Xijin, editor of the influential tabloid the Global Times, who wrote: "We will never be cowed by a handful of bad people."
China's nervousness about militancy, especially Islamic militancy, has grown since a car burst into flames on the edge of Beijing's Tiananmen Square in October, and 29 people were stabbed to death last month in the southwestern city of Kunming.
The government blamed Xinjiang militants for both incidents.
During his visit, Xinhua quoted Xi as saying: "The long-term stability of Xinjiang is vital to the whole country's reform, development and stability; to the country's unity, ethnic harmony and national security as well as to the great revival of the Chinese nation."
Uighurs have traditionally followed a moderate form of Islam but many have begun adopting practices more commonly seen in Saudi Arabia or Afghanistan, such as full-face veils for women, as China has intensified a security crackdown in recent years.
China reacted to the 2009 riots by pumping money into less-developed southern Xinjiang, in an implicit recognition of the economic causes of the unrest. But it has taken a much harsher line of late, especially towards dissenters.
The government detained Ilham Tohti, a Beijing economics professor who has championed Uighur rights, in January and subsequently charged him with separatism.
Advocates for Tohti say he has challenged the government's version of several incidents involving Uighurs, including the car fire on the edge of Tiananmen Square. (Editing by Robert Birsel and Robin Pomeroy)