TOBRUK, Libya  Vowing to track down and kill protesters “house by house,” Col. Muammar el-Qaddafi of Libya tightened his grip on the capital, Tripoli, on Tuesday, but the eastern half of the country was slipping beyond his control.

A bloody crackdown drove protesters from the streets of Tripoli, where residents described a state of terror. After a televised speech by Colonel Qaddafi, thousands of his supporters converged in the city’s central Green Square, wearing green bandannas and brandishing large machetes.

Many loaded into trucks headed for the outlying areas of the city, where they occupied traffic intersections and appeared to be massing for neighborhood-to-neighborhood searches.

“It looks like they have been given a green light to kill these people,” one witness said.

Human Rights Watch said it had confirmed 62 deaths in two hospitals after a rampage on Monday night, when witnesses said groups of heavily armed militiamen and mercenaries from other African countries cruised the streets in pickup trucks, spraying crowds with machine-gun fire.