MANILA — Rights advocates and survivors of the dictatorship of Ferdinand E. Marcos, the former Philippine leader, criticized President Rodrigo Duterte on Monday for saying that he could impose martial law to curb what he has called a runaway drug problem.

Mr. Duterte has made the war against illicit drugs a centerpiece of his administration. On Saturday, in a speech to business leaders in Davao City, in the country’s south, he warned that if the drug problem deteriorated into “something really very virulent, I will declare martial law.”

“No one can stop me,” he said. “My country transcends everything else, even the limitations.”

More than 6,000 killings across the Philippines have been linked to the antidrug campaign that began after Mr. Duterte took office in June. About 2,200 of those happened in encounters with the police, according to the Philippine National Police. The rest are classified as “deaths under investigation,” including those carried out by unknown vigilantes. More than a million people suspected of being drug users or dealers have also surrendered or been arrested.

“He has fascist dreams,” Loretta Rosales, 77, a former chairwoman of the Commission on Human Rights of the Philippines and a leftist politician, said of Mr. Duterte in an interview. She was detained and tortured under Marcos, who was elected president in 1965 and imposed martial law from 1972 to 1981. He was forced from power in 1986.