(CNN) At least three people were killed in Venezuela when clashes broke out during anti-government protests described by opposition leaders as the "mother of all marches."

Supporters of President Nicolas Maduro also held a counter rally Wednesday as opposition marchers gathered in the streets.

An hour into the march in Caracas, a 17-year-old boy was shot in the head, according to the Venezuela's public ministry, which said it had started investigating the incident. The teenager, later identified as Carlos Moreno, died while undergoing surgery, a hospital representative told CNN.

Moreno's sister, Alejandra, said Carlos studied economics at Venezuelan Central University in Caracas. Instead of joining the marches, she said, he was on the way to play soccer.

Video posted on social media showed a young man on the ground in the San Bernardino neighborhood -- a pool of blood near his head -- surrounded by marchers. A woman is heard yelling, "They've killed him."

Photos: Crisis in Venezuela Photos: Crisis in Venezuela A costumed demonstrator in Caracas, Venezuela, protests the government of Venezuelan President Nicolas Maduro on Sunday, August 6. Unrest continued to sweep through the country after a new legislative assembly was inaugurated following a controversial election on July 30. The new assembly has wide-ranging powers and is expected to rewrite the Venezuelan constitution at Maduro's behest. Opposition supporters, who see the vote as a power grab and an erosion of democracy, boycotted and staged demonstrations against the vote. Hide Caption 1 of 49 Photos: Crisis in Venezuela Soldiers stop a vehicle and detain its passengers on the Paramacay military base in Valencia, Venezuela, on August 6. According to authorities, two people were killed when an anti-government paramilitary attack was quelled at the base. Hide Caption 2 of 49 Photos: Crisis in Venezuela Anti-government activists stand near a flaming barricade in Valencia on August 6. Hide Caption 3 of 49 Photos: Crisis in Venezuela A man is arrested in Valencia during clashes between anti-government activists and the National Guard on August 6. Hide Caption 4 of 49 Photos: Crisis in Venezuela Members of the Venezuelan armed forces fly over Valencia in a helicopter while citizens demonstrate in support of a group that staged a paramilitary uprising at the Paramacay military base on August 6. Hide Caption 5 of 49 Photos: Crisis in Venezuela Venezuela's Chief Prosecutor Luisa Ortega Diaz, third from left, is surrounded by employees of the General Prosecutor's office as she is barred by security forces from entering her office in Caracas on Saturday, August 5. Hide Caption 6 of 49 Photos: Crisis in Venezuela Diosdado Cabello, a member of Venezuela's National Constituent Assembly, holds an image of Venezuela's late President Hugo Chavez as delegates gather for a group photo following their swearing-in ceremony on Friday, August 4. Hide Caption 7 of 49 Photos: Crisis in Venezuela Opposition activists protest against the newly inaugurated National Constituent Assembly on August 4. Hide Caption 8 of 49 Photos: Crisis in Venezuela A woman in Caracas attends a vigil Monday, July 31, for anti-government activists who have died in the country's recent unrest. More than 120 people have been killed in Venezuela since early April, according to the attorney general's office. Hide Caption 9 of 49 Photos: Crisis in Venezuela Opposition lawmaker Juan Requesens addresses a rally in Caracas on July 31. Two other leading opposition figures, Leopoldo Lopez and Antonio Ledezma, were rounded up from their homes, according to their families. Hide Caption 10 of 49 Photos: Crisis in Venezuela Maduro celebrates the results of a national vote on Sunday, July 30. His opponents boycotted the election and demonstrated against it for weeks, saying he orchestrated it to get around the existing National Assembly, which the opposition has controlled since 2015. Maduro has argued that the Constituent Assembly will help bring peace to a polarized country, with all branches of the government falling under the political movement founded by his late mentor and predecessor, Hugo Chavez. Hide Caption 11 of 49 Photos: Crisis in Venezuela Members of Venezuela's national police are caught in an explosion as they ride motorcycles near Altamira Square in Caracas on July 30. Venezuela has seen widespread unrest since March 29, when the Supreme Court dissolved Parliament and transferred all legislative powers to itself. The decision was later reversed, but protests have continued across the country, which is also in the midst of an economic crisis. Hide Caption 12 of 49 Photos: Crisis in Venezuela A wounded anti-government demonstrator is helped by medics during clashes with police in Caracas on July 30. Hide Caption 13 of 49 Photos: Crisis in Venezuela A demonstrator shouts slogans through a traffic cone during an anti-government protest in Caracas on July 30. Hide Caption 14 of 49 Photos: Crisis in Venezuela A protester wounded by a pellet gun receives attention July 30 during a demonstration against the vote for a Constituent Assembly. Hide Caption 15 of 49 Photos: Crisis in Venezuela A member of the National Guard fires at protesters during clashes in Caracas on Friday, July 28. Hide Caption 16 of 49 Photos: Crisis in Venezuela A demonstrator dressed as Venezuelan independence hero Simon Bolivar is silhouetted against a national flag in Caracas on Monday, July 24. Hide Caption 17 of 49 Photos: Crisis in Venezuela Venezuelan police Officer Oscar Perez joins in an anti-government protest in Caracas on Thursday, July 13. Perez allegedly piloted a stolen police helicopter used to attack the Venezuelan Supreme Court with grenades on June 27. Hide Caption 18 of 49 Photos: Crisis in Venezuela Venezuelan lawmakers Luis Stefanelli, left, and Jose Regnault appear stunned in a corridor of the National Assembly after a clash with demonstrators in Caracas on Wednesday, July 5. Supporters of Maduro stormed the building and attacked opposition lawmakers, witnesses said. At least seven legislative employees and five lawmakers were injured, according to National Assembly President Julio Borges. Journalists said they were also assaulted. Hide Caption 19 of 49 Photos: Crisis in Venezuela National Guard members clash with deputies of the National Assembly in the Parliament's courtyard in Caracas on Tuesday, June 27. Hide Caption 20 of 49 Photos: Crisis in Venezuela A boy runs under a national flag during a June 27 protest in Caracas. Hide Caption 21 of 49 Photos: Crisis in Venezuela Protesters tear down a fence at the La Carlota airbase outside Caracas on Friday, June 23. A soldier shot a demonstrator through the fence at the base on the previous day, killing him. Hide Caption 22 of 49 Photos: Crisis in Venezuela Hide Caption 23 of 49 Photos: Crisis in Venezuela Protester David Jose Vallenilla is shot through a fence by a member of the National Guard near a military base in Caracas on Thursday, June 22. Vallenilla later died in the hospital after suffering three gunshot wounds to the chest. Hide Caption 24 of 49 Photos: Crisis in Venezuela Maduro holds up a copy of the Venezuelan constitution during a news conference at the presidential palace in Caracas on June 22. Maduro has called for changes to the constitution amid the unrest. Hide Caption 25 of 49 Photos: Crisis in Venezuela A protester hides behind a barrier in Caracas on June 22. Hide Caption 26 of 49 Photos: Crisis in Venezuela An opposition activist displays bullet shells during an anti-government demonstration on Monday, June 19. Hide Caption 27 of 49 Photos: Crisis in Venezuela People flee during a clash between opposition demonstrators and riot police in Caracas on June 19. Hide Caption 28 of 49 Photos: Crisis in Venezuela Opposition activists aim projectiles toward riot police during a demonstration on June 19. Hide Caption 29 of 49 Photos: Crisis in Venezuela Demonstrators stand in front of a police vehicle on June 19. Hide Caption 30 of 49 Photos: Crisis in Venezuela A street in eastern Caracas is painted with the names of people killed during more than two months of protests. Hide Caption 31 of 49 Photos: Crisis in Venezuela During a "Grandparents' March" in Caracas, a man is blocked by police from reaching the Government Ombudsman's Office on Friday, May 12. Hide Caption 32 of 49 Photos: Crisis in Venezuela Opposition activists scuffle with riot police in Caracas on May 12. Hide Caption 33 of 49 Photos: Crisis in Venezuela Thousands of Venezuelan protesters march on a Caracas highway on Wednesday, May 10. Hide Caption 34 of 49 Photos: Crisis in Venezuela Opposition activists clash with riot police in Caracas on Monday, May 8. Hide Caption 35 of 49 Photos: Crisis in Venezuela Hide Caption 36 of 49 Photos: Crisis in Venezuela An armored National Guard vehicle runs over a protester in Caracas on Wednesday, May 3. The protester, 22-year-old Pedro Michell Yaminne, survived, his mother told CNN. Interior and justice minister Nestor Reverol told reporters that the "lamentable" incident was under investigation. He said that moments before Yaminne was run over, demonstrators hurled a Molotov cocktail at the armored vehicle, opened the side door and "brutally assaulted" the driver. Hide Caption 37 of 49 Photos: Crisis in Venezuela A demonstrator catches fire during protests in Caracas on May 3. It happened as protesters clashed with police and the gas tank of a police motorcycle exploded. Other photos from the scene showed the man being attended for burns to his body. Hide Caption 38 of 49 Photos: Crisis in Venezuela A demonstrator stands in front of an armored vehicle during protests in Caracas on Wednesday, April 19. Hide Caption 39 of 49 Photos: Crisis in Venezuela Opposition leader Henrique Capriles reacts to tear gas during a protest on April 19. Hide Caption 40 of 49 Photos: Crisis in Venezuela Riot police clash with demonstrators while tear gas fills the air in Caracas on April 19. Hide Caption 41 of 49 Photos: Crisis in Venezuela Rescue workers tend to a demonstrator hit by a tear gas canister during anti-government protests on April 19. Hide Caption 42 of 49 Photos: Crisis in Venezuela A demonstrator reacts during a march in Caracas on Saturday, April 15. Hide Caption 43 of 49 Photos: Crisis in Venezuela A protester suffering from the effects of tear gas is carried away on Thursday, April 13. Hide Caption 44 of 49 Photos: Crisis in Venezuela Clouds of tear gas spread across a highway in Caracas during clashes on Monday, April 10. Hide Caption 45 of 49 Photos: Crisis in Venezuela Demonstrators help a journalist whose leg was injured while covering clashes in Caracas on April 10. Hide Caption 46 of 49 Photos: Crisis in Venezuela Thousands of demonstrators protest against Maduro in Caracas on Saturday, April 8. Hide Caption 47 of 49 Photos: Crisis in Venezuela Venezuelan police line up before clashing with opposition activists on Thursday, April 6. Hide Caption 48 of 49 Photos: Crisis in Venezuela Demonstrators fight with national police officers in Caracas on Tuesday, April 4. Hide Caption 49 of 49

The ministry said it was also investigating the Wednesday afternoon shooting death of Paola Andreina Ramírez Gómez, 23, in plaza San Carlos in San Cristóbal, Tachira state.

Jorban Contreras, a paramedic and director of the civil protection unit in Tachira, said the woman lost a lot of blood and was already dead from a gunshot wound to her chest when he arrived.

In a third death, Venezuelan National Guard Sgt. Niumar Jose San Clemente Barrios was fatally shot Wednesday night, said the public prosecutor's office and Venezuela's top human rights official, ombudsman Tarek William Saab. A second guardsman was wounded by a bullet, the officials said. Both were shot during "violent protests" in the municipality of Los Salias, south of the nation's capital, according to Saab.

The public prosecutor's office has called for an investigation into the shooting.

Maduro: Don't complain when law comes after you

Maduro, who along with his supporters called for the countermarch, had deployed the Venezuelan armed forces to the streets on Sunday night amid rising tensions.

JUST WATCHED Venezuela turmoil escalates Replay More Videos ... MUST WATCH Venezuela turmoil escalates 01:33

He gave a fiery speech on Wednesday, accusing the opposition leaders of inciting violence. He called out the President of the opposition-controlled National Assembly, Julio Borges, saying "You are the head of the coup. Later, don't complain when the law comes after you."

Wednesday's marches underscored the widening political rifts in the country, where the opposition has accused Maduro of creating a dictatorship in the last few years. The government has repeatedly blocked any attempts by the opposition to oust Maduro from power by a referendum vote. It has also delayed local and state elections.

The opposition called for another march on Thursday, using the same strategy from the day before when protesters started their march at 26 different points throughout Caracas and converged at the office of the ombudsman, the government's top human rights official.

Government supporters and security forces on Wednesday succeeded in blocking marchers from reaching certain parts of the city, according to observers. Throughout the day, water cannons and tear gas canisters were unleashed on opposition marchers.

Video posted on social media showed marchers -- some covering their faces -- crossing the narrow Guaire River in the nation's capital in attempts to elude tear gas blasts.

1:06 PM Represión brutal y cobarde en la Autopista Francisco Fajardo. Estamos en el Río Guaire resistiendo pic.twitter.com/wETbeCu2xh — David Smolansky (@dsmolansky) April 19, 2017

The video was posted by David Smolansky, mayor of the municipality of El Hatillo and an opposition leader.

3:20 PM Así se resiste en pleno Guaire ante la represión cobarde de la dictadura. Los venezolanos salimos pacíficamente por nuestra libertad pic.twitter.com/5K70OjI70a — David Smolansky (@dsmolansky) April 19, 2017

In Washington, US Secretary of State Rex Tillerson expressed concerns to reporters Wednesday that the "government of Maduro is violating its own constitution and is not allowing the opposition to have their voices heard, nor allowing them to organize in a way that expresses the views of the Venezuelan people."

Colombian President Juan Manuel Santos said via Twitter on Wednesday that he had directed his country's exterior ministry to ask the UN Secretary General to address what he called the "worrying militarization of Venezuelan society."

What the opposition wants

The last vote held in Venezuela, the parliamentary election of 2015, gave the opposition a majority. Critics say any elections since have been delayed because Maduro is afraid of the outcome.

Then, on March 29, the Venezuelan Supreme Court dissolved the Parliament , transferring all legislative powers to itself. By doing away with the opposition-controlled legislative branch, the move effectively meant the remaining two branches of Venezuelan government were controlled by the ruling United Socialist Party. The opposition was outraged and called the move a coup. The decision was reversed three days later, but by that time protests had already erupted.

The protests have been bloody. Six people have died and countless others, many journalists, have been injured.

Thousands of people rally against Venezuelan President Nicolas Maduro along the Francisco Fajardo highway in eastern Caracas.

The opposition call became even stronger when, on April 7, the government notified main opposition leader Henrique Capriles that he had been banned from doing any political work for 15 years . The 44-year-old governor, who has run for president twice, said the government was again acting like a dictatorship.

Maduro, 54, has been defiant. Instead of taking steps to reduce tensions with the opposition, he has taken a confrontational tone with members of the opposition and protesters, whom he calls "vandals and terrorists."

Opposition leaders have called for the National Assembly's powers to be fully restored, for all the political prisoners to be freed, for a humanitarian corridor to be opened and for the stalled elections to take place.

A troubled economy

Unemployment, meanwhile, is set to surpass 25% this year, possibly on its way to 28% next year. It was at 7.4% in 2015.

Venezuela's economy shrank 18% last year, its third year of recession. It is expected to be in the red this year and next.

When there is food and water on the shelves, prices are so high that few Venezuelans can afford it. Many have taken to eating out of the trash.