The Philippine president has acknowledged for the first time that he may not be able to keep his campaign promise to eradicate illegal drugs in three to six months because of the enormity of the problem.

President Rodrigo Duterte said late Sunday that he may need to extend his self-imposed deadline by another six months to end the scourge. He said that with the huge number of people, including government officials, who are involved in the crime, "even if I wanted to, I cannot kill them all."

More than 3,000 suspected drug dealers and traffickers have been killed under Duterte's bloody campaign against drugs since he assumed the presidency in June.

President Barack Obama, U.N. officials and human rights watchdogs have raised concerns over the widespread killings.