Six suspects arrested in connection with the assassination of Ecuadorian presidential candidate Fernando Villavicencio are Colombian nationals and gang members, authorities have confirmed, as a former vice president demanded action over spiraling levels of violence in the South American country.

Villavicencio, an anti-corruption campaigner and lawmaker who was outspoken about the violence caused by drug trafficking in the country, was shot dead at a campaign rally in the capital Quito on Wednesday.

The killing of the 59-year-old came 10 days before the first round of the presidential election was set to take place. Villavicencio's campaign had promised a crackdown on crime and corruption amid a deadly escalation of violence that has gripped Ecuador in recent years.

The suspected shooter died in police custody following an exchange of fire with security personnel, Ecuador's Attorney General's Office said Wednesday.

Six others were arrested in connection with the killing. Ecuador's Interior Minister Juan Zapata said in a news conference Thursday that the suspects are members of organized criminal groups, citing preliminary evidence.

He later confirmed to CNN the suspects are Colombian nationals. The nationality of the suspected gunman is not yet clear.

During overnight raids, authorities found a rifle, a machine gun, four pistols, three grenades, two rifle magazines, four boxes of ammunition, two motorcycles, and a stolen vehicle believed to have been used by the men, Zapata said.

The attack prompted Ecuador's President Guillermo Lasso to request help from the US Federal Bureau of Investigation, and he tweeted that a delegation would soon be arriving in the country.

Lasso also announced a state of emergency for 60 days, an immediate mobilization of the armed forces across the country and three days of national mourning.

The assassination prompted an outpouring of condemnation from inside Ecuador and around the world, including from the UN Human Rights chief, the United States and European Union.

On Friday, a judge ordered the preventive detention of the six Colombian nationals detained under suspicion of Villavicencio's murder, the Ecuadorian Prosecutor's Office said in a statement. The Prosecutor's Office said the investigation into the suspects will last 30 days.

Level of violence 'something we have never seen before'

The former vice president of Ecuador and current presidential candidate Otto Sonnenholzner said in an exclusive interview with CNN Thursday that the level of violence in Ecuador is "something we have never seen before."

"It's something new. It started maybe one and a half or two years ago. It's a spiral of violence that is completely out of control and demands concrete government action that we are not seeing," Sonnenholzner said.

The Andean country, a relatively peaceful nation until a few years ago, is now plagued by a deteriorating security crisis fueled by drug trafficking and a turf war between rival criminal organizations.

Violence has been most pronounced on Ecuador's Pacific coast as criminal groups battle to control and distribute narcotics, primarily cocaine.

The country has also lost control of its overcrowded prisons, which are often ruled by criminal gangs. Hundreds of inmates have been killed in brutal prison riots between these rival gangs.

"The gangs are controlling crime in the streets from the jails," Sonnenholzner said. "There is a lot of influence of drug dealers and drug traffickers in different institutions in the country," including corruption affecting the judiciary, some police, and even local governments across Ecuador, he said.

Sonnenholzner told CNN that Villavicencio had received threats two weeks ago from organized crime groups in Ecuador, but he had not been protected.

Villavicencio did have a security detail at the time of the shooting, comprised of five police officers, multiple patrol cars, and his own armored vehicle, according to interior minister Zapata, though he noted that the armored vehicle was not used in Quito.

Seven of Ecuador's eight presidential candidates were under police protection, Zapata said earlier in the week, according to local media.

"Gun control is completely failing every day. The guns that the criminals are carrying are relatively new... The six people who were detained yesterday, that were part of the attack -- they had machine guns and grenades and Ecuador has been historically a very peaceful country," Sonnenholzner said.

Sonnenholzner said he had suspended public campaign events "for the next few days" and had taken on his own private security.

Ecuador's presidential election, scheduled for August 20, will go ahead as planned, the Electoral Council President Diana Atamaint said Thursday.

Sonnenholzner said he has requested the televised presidential debate planned for Sunday be postponed so Villavicencio's political party, Movimiento Construye, has time to find a new candidate.

He noted that Villavicencio had first entered public life as an investigative journalist who fought against corruption and abuses of power.

His "fight against corruption should be his legacy," Sonnenholzner said.