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CARACAS, Venezuela — Opposition leader Juan Guaido's calls for Venezuelans to abandon Nicolas Maduro's government are booming across the world outside, but the self-declared interim president is having a harder time delivering his message at home.

Watchdog groups in Venezuela and abroad say Guaido's efforts to reach citizens via the internet have been hindered by the dominant provider — state-run CANTV — in a country where critical newspapers and broadcast media already have been muzzled.

Since Jan. 23, when Guaido proclaimed himself interim president and when protests against Maduro's rule broke out, CANTV has blocked access to social media sites at least four times, according to the monitoring groups.

Those disruptions have coincided with politically significant events, including a rally attended by thousands of people last week and a Sunday night speech that Guaido livestreamed on Periscope to call for a new round of protests and urge members of the military to defect.

CANTV accounts for about 70 percent of Venezuela's fixed internet connections and 50 percent of mobile, and Netblocks, a non-government group based in Europe that monitors internet censorship, found that the government provider blocked Facebook, Instagram, Twitter and YouTube during 12 of the 13 minutes that Guaido's speech lasted, so the stream could only be seen without interruptions by people using privately run internet providers.

The organization runs tests from its headquarters with software that captures evidence of connection failures. It also has designed a scanner app that volunteers in affected countries can use to run tests from their own phones or computers.

"We built tools that could diagnose the problems and differentiate between overload disruptions and actual blocking," said Netblocks director Alp Toker.

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VESinFiltro, a Venezuelan internet monitoring group that uses technology developed by the Open Observatory for Network Interference, published similar findings on the Sunday night speech.

Rights groups say the targeted disruptions show that methods to silence critics are becoming increasingly sophisticated in Venezuela, where internet providers have been hindering access to news sites and illegal currency exchange sites since 2014.

VESinFiltro director Andres Azpurua said that while internet providers previously restricted access to websites through a technique known as DNS blocking, methods have evolved to allow just-in-time disruptions during different stages of a computer's connection to websites, making it harder for site administrators to evade.

He also said other civil liberties advocates have been urging Venezuelans to try to avoid blockages by using virtual private network software that encrypt data and often hide the origin of a connection, and he said use of VPNs has increased over time.

A study by Venezuela's Press and Society Institute found that 53 websites were partially blocked by internet providers in Venezuela last year, including an investigative news site and the website for one of the country's last remaining opposition newspapers. Analysts say that this year, Guaido's Wikipedia page, and social media sites have suffered blocks.

"The previous modus operandi was to place long-term blocks on certain web addresses," Azpurua says. "But the most recent forms of blocking are more tactical. You can tell that someone is investing in the technology to do this." While some analysts have speculated the know-how could come from Russia, Toker points out that technology developed by Western countries to block sites run by terrorist groups can also be reconfigured to block other sites.

Social media include some of the few platforms where Guaido can still be seen by Venezuelans. Local television and radio stations, fearful of government sanctions, have generally refrained from airing opposition rallies for years and avoid interviews with Guaido. A nationally broadcast radio program hosted by journalist Cesar Miguel Rondon was cancelled after it covered last week's turmoil and discussed Guaido's claim to Venezuela's presidency.

The opposition leader argues that Maduro's re-election in May was fraudulent and with no legitimate president, the constitution gives him power to be interim leader because he is head of the congress. The Trump administration and a dozen other countries have recognized Guaido as the country's rightful leader.

The Venezuelan government has previously ordered some internet news content to be blocked, claiming it is defamatory. It has also banned some news networks from cable systems, arguing they violated communication laws.

Venezuela's telecoms regulator and the Ministry of Communication did not respond to requests for comment on the most recent blocks on social media sites.

Technical interference isn't the only problem for internet users in Venezuela, where social media are rife with campaigns of false information benefiting both the government and the opposition.

Twitter last week removed 1,900 accounts located in Venezuela as part of a broader purge of international accounts tied to misinformation campaigns.

Twitter's head of site integrity, Joel Roth, wrote that many of the deleted Venezuelan accounts appeared to be engaged in a "state-backed influence campaign targeting domestic audiences."

Mariengracia Chirino, a researcher at the Venezuelan Press and Society Institute, said that access to information is also hampered by Venezuela's low bandwidth, as telecommunications infrastructure crumbles in the economically struggling nation.

The average connection speed in Venezuela is 1.8 mpbs, which is less than half the average speed in Latin American countries. Chirino said that her organization conducted tests during the Jan. 23 protests that found connection speeds dropping to an average rate of 0.9 mbps, making it difficult to share videos.

"During the protests, we also registered temporary blocks on Google sites like Gmail and YouTube," Chirino said.