Programmer and cyberactivist Jose Luis Rivas said the Internet went out in most of the city of 600,000 about midnight Wednesday.
Since protests accelerated last week, activists have posted YouTube videos of riot police and National Guard breaking up demonstrations and, they claim, firing at unarmed civilians. Sometimes, the security forces are accompanied by pistol-packing motorcycle gangs of Chavista loyalists.
Rivas said that on Wednesday night, before the Internet went out in San Cristobal, people were live-streaming video of a crackdown by security forces.
Cutting off Internet deprived people of their only access to uncensored information and Rivas said people told him "they felt fear because they were no longer informed."
On Friday, the state news agency AVN quoted Science and Technology Minister Manuel Fernandez as blaming the Internet outage in Tachira on "severing of fiber optic lines by accident in some cases and in others from vandalism."
Hacktivists also have been attacking government websites and Fernandez said Friday in a TV interview that 147 had been defaced or rendered unreachable with denial-of-service attacks, or data-packet floods, over the previous 11 days.
He said many had been restored, but the state television network's site, vtv.gob.ve, remained offline Friday night.
Images, meanwhile, were visible again on Twitter after last week's outage.
Company spokesman Nu Wexler said Thursday that measures which he did not specify were taken to "ensure continuity of service."
Twitter also continued to tweet a workaround that lets users in Venezuela receive tweets on their cellphones via text message.
Government officials have accused "putschists" of spreading disinformation via social networks as part of what they claimed is a coordinated campaign to overthrow the government.
Even before the protests, which have claimed at least six lives since Feb. 12, Venezuela had been blocking websites that track the black market rate for the country's currency. For several weeks, that knocked out access to the popular Web address-shortening application Bitly.
Venezuelans who want to reach such sites are increasingly using proxy services, which have long been employed by people in China and Iran to circumvent government censors.
The international director of the Electronic Frontier Foundation, Danny O'Brien, said he thought Venezuelan net censorship has been "somewhat haphazard and arbitrary."
Nearly half Venezuela's population relies on government-controlled media as their sole information source, the rest on the Internet.
But cutting off Internet is not smart political strategy, said O'Brien.
"I think the important lesson people should learn from these Internet blackouts is that they just throw fuel on the flames of civil unrest."
Frank Bajak on Twitter: http://twitter.com/fbajak