The Central American country declared the emergency measures -- allowing the arrest of gang members without a warrant -- last week after 87 reported killings from March 25 to 27.
And on Monday the president said the 6,000 detained in a little over a week added to the 16,000 gang members already incarcerated in El Salvador's prisons.
Speaking at a police barracks in the capital San Salvador, Bukele addressed public concerns of gangs "taking revenge" on the population due to the massive arrest operations.
If they commit an act of revenge, "there will not be even one meal in the prisons," the president said.
"I swear to God that they will not eat a single grain of rice, and we will see how long they last, and I don't care what international organizations say," he added.
Besides arrests without a warrant, the emergency measures -- which last one month -- also restrict freedom of assembly, while telephone calls and emails can be intercepted without a court order.
Such broad and swift enactment of powers granted to the military and police has drawn alarm from local and international human rights organizations.
Bukele added that he had ordered the construction of a maximum-security prison with a capacity of 20,000 inmates.
"There are only two ways: jail or death," he said.
The 40-year-old president, elected in 2019, enjoys broad support in El Salvador over his promises to fight organized crime and improve security in the violence-wracked country.
Last week, the ruling party-controlled parliament reformed the penal code to increase the maximum sentence for gang membership from nine to 45 years in prison.
