Blogger Nguyen Hue Chi is locked in an electronic game of cat and mouse with a mystery cyberattacker -- widely believed to be the government.

Chi and his colleagues have set up a series of websites and blogs questioning government policy in the past year, only to see them attacked and blocked.

Observers blame the communist state, which they say has adopted a more aggressive stance towards politically sensitive Internet sites.

"It seems that the government is definitely starting to follow the China model," said a foreign diplomat who asked for anonymity.

"The simple fact is, where they used to just try to block access, now they try to take down the websites."

According to the diplomat's count, about 24 websites have been disrupted this year.

Bauxite Vietnam, which Chi administers, was one of them.

The website last year initiated a petition against government plans for bauxite mining in the country's Central Highlands, helping to fuel a rare public outcry from a broad spectrum of society.

The project, now underway, is controversial partly because at least one Chinese company has been granted a major contract.

"It's clear that they have followed the Chinese model of controlling the Internet," said Chi, which has also criticised the government over a sea dispute with China.

Beijing operates a vast system of Web censorship, sometimes referred to as the "Great Firewall of China".

Chi said two blogs and a website established in April last year were all blocked by year's end, "despite great resistance", and three new sites became overloaded from "hundreds of thousands" of attacks.

Bauxite Vietnam is still accessible, however, through two blogs. And Chi vowed to defend his websites "until the end."

In March, US-based Internet giant Google said hackers had specifically "tried to squelch opposition to bauxite mining efforts in Vietnam".

Those responsible might have had "some allegiance" to the Vietnamese government, said California-based Internet security firm McAfee.

The incidents recalled cyberattacks in China that Google in January said had been a bid to hack into the email accounts of Chinese human rights activists.

Google stopped censoring its search engine results in China, as is required by the government for it to operate.

Google also issued a warning on Vietnam in June, saying it was troubled by new regulations that may allow the government to block access to websites and track the activities of Internet users.

But Vietnam's Ministry of Foreign Affairs responded that soaring rates of Internet use have brought "challenges" such as violent content and pornography, particularly at public Internet businesses.

"This decision is aimed at guaranteeing safety and healthy usage for Internet users at public Internet access points in Hanoi," said ministry spokeswoman Nguyen Phuong Nga.

She said concerns over free expression are groundless.

Vietnam's Internet growth is among the world's fastest, and users number almost 24 million or about 28 percent of the population, Nga added.

Observers said Vietnam stepped up its campaign when it allegedly began blocking Facebook, the world's most popular social networking site, in November. Users are still unable to log in through the site's homepage, but many have found other ways to access the site.

Access to the BBC's Vietnamese language website has also been hit.

These restrictions, and on news media, led Western donors in December to say Vietnam's actions threatened its rapid economic progress.

A second diplomat, who also asked for anonymity, said that despite its efforts, the government will face difficulties controlling the Internet.

"You can close down Facebook and you can close down YouTube but there will always be ways for people who really want to, to get around it," said the diplomat.

Blogging has fast risen in popularity since it entered Vietnam in 2005. The government began to clamp down last year even though only a small percentage of commentators are focused on politically sensitive issues, said one blogger.

"I think last year was a big milestone," the blogger, who requested anonymity, said.

Vietnamese security agencies have "exponentially" raised their Internet monitoring ability "because that's the space the dissidents have moved into," said Carl Thayer, a Vietnam specialist with the University of New South Wales.

"They're acquiring and absorbing into their capabilities very modern stuff," partly with help from fellow-communist China which faces similar threats from cyber dissidents, he said.

The sensitivity of Internet conversation has been heightened by next year's Communist Party Congress, a five-yearly event that determines high-ranking leadership posts, Thayer added.

Key documents will be released for public comment before the Congress, and the Party wants to prevent that discussion "from being hijacked" by dissidents, he said.

New York-based Human Rights Watch accused Vietnam in May of a sophisticated and sustained attack against online dissent.

It said at least seven independent bloggers had been detained over the previous two months.