The four died in and around Cali on Friday as tens of thousands marched across the country in the latest in demonstrations that started on April 28 to oppose tax reform but have since expanded to include wide-ranging demands.

Talks between the government and the protest leaders, including union leaders who have formed a national strike committee, have stalled.

"From tonight begins the maximum deployment of military assistance to the national police in Cali and the province of Valle," Duque said in a televised message.

He added that more than 7,000 personnel will be sent to lift road blockades, including members of the navy, but did not give any more specifics.

Clara Luz Roldan, governor of Valle del Cauca, earlier declared a curfew would start in the province from 7:00 p.m.

On Friday in Cali, an epicenter of the protests, Mayor Jorge Ospina confirmed three deaths. Local media reported the fourth death occurred on the road between Cali and the town of Candelaria.

Two people in Cali were killed when an agent of the attorney general's investigative unit opened fire on civilians, before also being killed, Attorney General Francisco Barbosa said in a televised message. The agent was not on duty at the time, Barbosa said.

The demonstrations have been plagued by violence.

As of Thursday 17 civilians have died in connection with protests, the government said. Human rights groups say dozens more have been killed by security forces. Two police officers were also earlier reported killed.

Human Rights Watch's executive director for the Americas, Jose Miguel Vivanco, said on Twitter the advocacy group had verified videos published on social media showing armed men in civilian clothes firing weapons while police look on.

Vivanco called on Defense Minister Diego Molano to explain. Colombia's defense ministry did not immediately respond to questions.

DEMANDS

The demonstrations have pressured the government and lawmakers into shelving the tax and health reforms and prompted the resignation of former finance minister Alberto Carrasquilla.

Protester demands now also include a basic income, opportunities for young people and an end to police violence.

Although demonstrations outside Valle del Cauca on Friday were mostly peaceful, clashes between police and protesters were reported in some areas, such as the municipality of Madrid, near Bogota, as were incidents of violence in the city of Popayan.

Amid singing and music in the capital Bogota, protesters said they would keep marching.

"Until the government listens to us, we have to stay in the streets," Alejandro Franco, 23, told Reuters. Close to graduating, he said he was marching for better education and health, among other reasons.

"If the people don't have peace then neither will the government," he added.

Despite the government and protest leaders reaching a "pre-agreement" for ending demonstrations this week, strike organizers on Thursday said the government had not signed the deal and accused it of stalling. read more "We have already reached the agreement, the only thing missing is the president's signature to start the negotiations," Francisco Maltes, president of the Central Union of Workers (CUT), said on Friday, accusing the government of delaying talks.

The government said it had not signed the deal because some protest leaders would not condemn road blocks, calling the issue non-negotiable, and adding that talks will resume on Sunday.

Colombia's finance ministry estimates protests and roadblocks have cost the country $2.68 billion, with the roadblocks leading to shortages of food and other supplies, boosting prices, and disrupting operations in the country's main seaport as well as for hundreds of companies.

"I have to close my shop every time there are protests," Laudice Ramirez, 62, said in the south of the city. "I'm going bankrupt, but the youth don't have any other options for opportunities."