Protesters thronged the main avenues of Caracas and other Venezuelan cities, braving bullets, tear gas and militant supporters of President Nicolas Maduro in the biggest show of opposition to his rule in months.

The miles-long Caracas demonstration was called “the mother of all marches” by organizers, who rallied demonstrators from 26 points in Caracas. Opponents also took to the streets of cities including Barquisimeto, Porlamar and Maracaibo, where they were met by national guard and local police. At least two protesters were shot dead in the capital and the western city of San Cristobal.

“Today without fear millions of Venezuelans mobilized to defend the constitution,” opposition governor and two-time presidential candidate Henrique Capriles said in an emailed statement. Later this evening, Caprilles called for supporters to congregate at the same meeting points nationwide, including 26 locations in Caracas, on Thursday for a second day of protests.

Ricardo Rios, a mathematics professor at Central University in Caracas, said that today’s march, organized by a coalition of opposition parties, was larger than the last major demonstration in September. At least 1.2 million people filled 12 miles of streets and highways, he said. Neither the government or opposition published exact figures.

Thousands of supporters of Maduro also rallied downtown, with state television showing trucks distributing water bottles on a hot day and an inflatable balloon in the form of the late President Hugo Chavez.

Maduro and his supporters retain a potent capacity to resist.

Caracas-based newspaper El Nacional reported that a 17-year-old died after being shot in the head by presumed government supporters known as “colectivos” early in the morning. It also reported the death of a 23-year-old woman shot by colectivos in San Cristobal. About 50 people were detained across the country and an unknown number injured, according to Provea, a human rights nongovernmental agency.

‘Constitutional Right’

Lilian Tintori, wife of jailed opposition leader Leopoldo Lopez, wore a protective mask as she waved a Venezuelan flag and walked toward a gas cloud, an image captured in a video posted on her Twitter account. In the afternoon, tear-gas barrages extended into parts of eastern Caracas that are opposition strongholds.

The mobilization comes as Maduro faces scrutiny abroad and within his own government after the country’s top court last month tried to grab power from the opposition-controlled congress. The opposition is trying to strengthen its momentum after its attempt last year to oust Maduro with a referendum was quashed by election officials.

Venezuela’s public prosecutor, Luisa Ortega, a member of the ruling Socialist party, urged security forces to guarantee the ability to dissent.

“It is a constitutional right to call for peaceful protests, and they should not put the physical safety of protesters at risk,” she said in a statement on Twitter.

Government Repression

Fears of violence spiked this week after Maduro said he would increase the size of a citizen militia that supports the government to 500,000 members and give each cadet a gun. At a rally this afternoon where he sang and danced with other government officials, Maduro accused Julio Borges, the president of the opposition-controlled National Assembly, of trying to foment a coup and blamed him for the day’s violence.

“Today they tried to defeat a power, and they failed again,” Maduro said. “Julio Borges, don’t complain when justice comes for you.”

Still, Maduro said that he was willing to hold talks with the opposition even after today’s clashes.

Maduro’s government has been increasing its suppression of protests over the past weeks, with Caracas-based nongovernmental agency Foro Penal reporting five deaths and at least 538 arrests at protests this month.

“After today’s march, the risk of violence will continue as the government is determined to maintain its power and close the electoral path,” said Maria Teresa Urreiztieta, a social psychologist at Simon Bolivar University in Caracas. “The challenge for the opposition now is to build collective leadership that can channel popular demands.”

U.S. Secretary of State Rex Tillerson said today in Washington that the U.S. was “concerned” about the situation.

‘Tipping Point’

Maduro has rarely appeared more vulnerable since his election in 2013 after the death of his predecessor Chavez. Criticism has mounted abroad and at home as the country continues to grapple with years of economic contraction, the world’s fastest inflation and widespread shortages of food and medicine.

The president retains one powerful ally: the armed forces.

“The military has strong economic incentives to hold Maduro in power,” Diego Moya-Ocampos, an analyst at IHS Markit, said in an emailed note. “Nevertheless, if sustained and prolonged strong protests reach a tipping point by overwhelmingly escalating beyond the capacity of security forces to contain them, then the probability of the military changing its stance and forcing the National Electoral Council to hold early elections or stage a coup to assume power directly will increase.”