A group of around 20 men attacked on early Sunday a military base in Venezuela’s third largest city, as President Nicolas Maduro vowed to lay down the “maximum penalty” against the perpetrators.

Led by an army officer, the group made off with weapons after a three-hour attack on the Paramacay base in the central city of Valencia on early Sunday, officials said.

The raid ended with two of the attackers being killed and eight captured, Maduro said on state television. The other 10 escaped with weapons taken from the facility, according to officials who said an “intense search” was underway for them.

Maduro said that the military was hunting down the “mercenaries,” claiming the “terrorist” group had ties to Colombia and the United States.

The armed forces said in a statement “a group of civilian criminals wearing military uniforms and a first lieutenant who had deserted” carried out the attack.

In a video posted online just before the attack, a man presenting himself as an army captain named Juan Caguaripano declared a “legitimate rebellion… to reject the murderous tyranny of Nicolas Maduro.”

Speaking with 15 men in camouflage standing by him, some of them armed, he demanded a transitional government and “free elections.”

It was not known if he was the lieutenant referred to in the military statement, demoted for deserting, or whether he was another renegade officer.

That statement said the lieutenant involved had deserted three years ago and taken refuge in Miami, in the US state of Florida.

In 2014, Caguaripano released a 12-minute video denouncing Maduro during a previous wave of anti-government unrest. He later reportedly sought exile after a military tribunal ordered his arrest, appearing in an interview on CNN en Espanol to draw attention to what he said was discontent within military ranks.

Maduro said the lieutenant, among those captured, was “actively giving information and we have testimony from seven of the civilians.”

Maduro congratulated the army for its “immediate reaction” in putting down the attack, saying they earned his “admiration.”

Venezuela’s opposition has repeatedly urged the military to abandon Maduro.

But Defense Minister Vladimir Padrino, the head of the armed forces, has said the military’s loyalty was unshakable.

The incident heightened fears that Venezuela’s deepening political and economic crisis could explode into greater violence, perhaps open armed conflict.

Officials insisted afterward that all was normal across the country.

Military helicopters flew overhead and tactical armored vehicles patrolled the streets in Valencia in a climate of tension on Sunday after the attack.

Locals said a nighttime curfew was imposed. Police dispersed protesters who had set up flaming barricades across roads.

Venezuela has become increasingly isolated internationally as Maduro tightens his hold on power through a contested loyalist assembly that started work this week.

The opposition, which controls the legislature, has been sidelined. Its leaders are under threat of arrest after organizing protests — fiercely countered by security forces — that have left 125 people dead in the past four months.

The new Constituent Assembly, packed with Maduro allies including the president’s wife and son, has quickly used its supreme powers to clamp down on dissent.

On Saturday, it ordered the dismissal of the attorney general, Luisa Ortega, who had broken ranks with Maduro to become one of his most vociferous critics.

The United States accuses Maduro of installing an “authoritarian dictatorship” that has turned Venezuela into an international pariah. The United States, Brazil, Colombia, Chile, Guatemala, Mexico, Panama and Peru have slammed the “illegal” sacking of Ortega.

And Argentina, Uruguay, Paraguay and Brazil have indefinitely suspended Venezuela from the South American trading bloc Mercosur for its “rupture of the democratic order.”

The constitutional assembly is expected to meet again Tuesday, while lawmakers in the opposition-controlled National Assembly scheduled their own session for Monday, vowing to continue fulfilling their responsibilities no matter what the assembly might do. Leaders of opposition groups, which boycotted the July 30 assembly election, called for renewed protests on Monday, though turnout at demonstrations has been sparse in recent days.