SAN SALVADOR (Reuters) - President Nayib Bukele and a group of soldiers armed with automatic weapons briefly occupied El Salvador’s Congress on Sunday, stepping up a pressure campaign to force lawmakers to back a crime-fighting plan.

Watched by soldiers in full battle uniform, Bukele, 38, sat in the seat reserved for the president of Congress and cupped his hands together to pray, he said, for patience with lawmakers, few of whom turned up at the special session.

“If those shameless people don’t approve the plan of territorial control, we’ll summon you here again (next) Sunday,” he told supporters in a fiery speech outside, as he left the building.

Lawmakers were due to meet on Monday to discuss the president’s proposals, Congress president Mario Ponce said, in a possible sign of de-escalation.

Critics warned of a looming constitutional crisis, however. Human Rights Watch, a U.S.-based group, called the event “an exhibition of brute force” and said the Organization of American States should urgently meet to discuss the situation.

Bukele won office last year after a savvy social media campaign feeding off popular discontent with two parties that had ruled the Central American country since the end of a civil war.

Channeling that same frustration with traditional parties, he attacked Congress for foot-dragging over approval of a $109 million multi-lateral loan he has sought to equip police and soldiers to fight crime.

His cabinet called Sunday’s special session after Bukele said on Friday that Salvadorans had a legal right to insurrection in such situations, calling for protests and briefly removing lawmakers’ security protection details.

The president’s move to pressure lawmakers was backed by defense minister René Merino Monroy and police director Mauricio Arriaza Chicas.

However, El Salvadoran think-tank FUSADES said there were no grounds for the executive branch to call such a session, since Congress was functioning normally.

On Sunday, hundreds of Salvadorans responded to Bukele’s call to demonstrate, waving banners and blowing whistles outside Congress, as soldiers and police officers stood by to protect them, a Reuters witness said.

“We are here because of the insecurity we have in our country, and the lawmakers do not want to recognize that,” said Adelma Campos, a 43-year-old housewife. “They do not want to work for the people who gave them their votes.”

Although the murder rate in El Salvador has declined steeply since Bukele took office, authorities continue to battle gangs that control vast territory in the Central American country.

In a statement, the United Nations High Commissioner for Human Rights called on Sunday for “dialogue and full respect for democratic institutions to guarantee the rule of law, including the independence of the branches of public power.”