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.