Opponents of Nicolás Maduro face off against troops loyal to the government on Tuesday. (Ariana Cubillos/AP)

Venezuela’s state-run Internet service on Tuesday appeared to cut off broad swaths of the nation’s social-media and messaging sites, taking aim at the most critical ways Venezuelans had organized protests and communicated with family amid military clashes and violent unrest.

Internet-monitoring groups said CANTV, the state-run Internet provider through which most people access the Web, appeared to block or restrict access to a range of websites, including Twitter and Instagram, that opposition leader Juan Guaidó and other groups have used to mobilize growing protests against President Nicolás Maduro.

The video giant YouTube, the search engine Bing, the live-streaming video service Periscope, and chat and messaging services run by Google also appeared to be blocked as part of the latest sweeping move by an authoritarian regime to squash online dissent.

The blocks contributed to the chaos of a challenge spearheaded by Guaidó and backed by an unknown number of soldiers as thousands of protesters clashed in the streets with pro-government militias and Maduro loyalists. But the cutoff did not entirely disrupt the uprising, and many Guaidó supporters in the streets said that the networks had first alerted them to the protests.

"In the Venezuela we are living today, social media is vital," said Veronica Caña, a 40-year-old woman who was at the eastern Caracas highway on Tuesday morning heading to join the Guaidó protests. "I woke up at 5 a.m. and I started to receive information of what was happening in La Carlota and, well, my whole scheduled plans for the day changed. I had to do my duty and join."

Governments facing political turmoil often seek to shut off all or some of the Internet access in their countries to hinder organizing by opponents and the spreading of information that might fuel protests. The Egyptian government in 2011, for example, blocked overall Internet access during the Arab Spring uprisings for nearly a week.

More often, though, national governments seek to block social media and other communication tools while keeping online the overall Internet, which can be essential to commerce and government operations. Sri Lanka, for example, blocked some social media sites after the Easter Day bombings that left hundreds of people dead, and restored access to the sites two days later. Monitoring services reported that the Internet in Venezuela, though spotty in places, remained functioning Tuesday amid the blocks to social media services.

Blocking individual services, such as major social media sites, is technically easy when there are only a few major telecommunications providers in a country, though individual users can sometimes evade such roadblocks using software tools such as virtual private networks, or VPNs, that allow a user to obscure the origin of their Internet use.

Michael Camilleri, a director at the Washington-based think tank Inter-American Dialogue, said social-media and online messaging services had become the most critical ways Venezuelans communicated beyond the reach of government censors. The opposition to Maduro has publicly mobilized on Twitter and Instagram and privately communicated through group chats on the encrypted messaging service WhatsApp.

But Maduro’s attempts at an “information monopoly,” and the Internet restrictions that have followed, have hampered people’s ability to understand the state of a country suffering growing violence and near-total economic collapse. For news on the unrest, many Venezuelans had to rely on family members back in the U.S. messaging them via WhatsApp.

“The Venezuelan government going back years now has essentially co-opted or silenced any independent media in the country. So the Internet has become an essential source of information for anybody who doesn’t want to take government propaganda as truth,” he said.

If “there's a democratic revolution in Venezuela,” he added, it will be one that “was very much organized and inspired by these” networks.

NetBlocks, a Europe-based watchdog group that tracks Internet censorship, said their tests found that social-media services, independent news sources and other sites appeared to be blocked in a way that could not be explained by outages or other natural disruptions.

Some VPN services, such as the public VPN app TunnelBear, also appeared to be taken offline. VE sin Filtro, a Venezuelan-based firm that also tracks Internet blocks, said its tests found similar interference.

Alp Toker, the executive director of NetBlocks, said the blackouts began early Tuesday and proceeded through three distinct phases, beginning with brief disruptions to Twitter and video-streaming sites and concluding with a mass degradation of some of the country’s most-used services, including Instagram. “There’s impact across the board,” he said.

Twitter has been a key network for both sides of the Venezuelan crisis. Maduro’s communications minister tweeted Tuesday that government forces were confronting a “coup” in the capital launched by a “reduced group of military officials who are traitors.”

But the platform also helped drive protesters such as Leonel Mendoza into the action. “I saw it on Twitter and decided to go to the street right away,” said Mendoza, 29.

Guaidó's team has struggled to reach the masses because most TV and radio stations are censored by a pro-government regulatory agency, CONATEL, and most newspapers have been bought over the years by sympathizers of the socialist government of the late president Hugo Chávez. Many international outlets have been banned, dozens of radio stations have been closed, and state-run TV networks largely transmit propaganda by the Maduro government. NetBlocks said YouTube, Periscope and other sites also have been blocked in recent weeks during Guaidó's speeches; they were generally brought online shortly after the speeches ended.

Opposition leaders inform their supporters and call for protests through Twitter and Instagram, and relay messages through WhatsApp. To reach people in the slums and remote areas where Internet access is limited, Guaidó's team has also launched an election-style grass-roots campaign, dubbed “Operacion Libertad,” designed to boost their social-media reach.

“The defense of democracy is also led through social media," Guaidó tweeted on Monday through an account, @Presidencia_VE, through which he said all official information would be announced. “Let’s spread this new channel of official information, this window of freedom,” he said.

Craig Timberg contributed to this report.