CARACAS, Venezuela — Venezuela’s National Assembly erupted into chaos on Tuesday as opposition lawmakers took their seats to begin the new year’s session, but only after forcing their way through a phalanx of government soldiers.

National Guardsmen in body armor initially prevented Juan Guaidó, the leader of the country’s opposition, from entering the building along with his supporters.

“Here the people rule!” the legislators cried as they pushed through the heavy wooden doors and installed Mr. Guaidó at the front of the assembly’s main hall.

When it was all over, Mr. Guaidó said he would continue to claim the country’s presidency and he called for a new round of protests, starting Thursday, designed to oust the country’s authoritarian leader, Nicolás Maduro.