Metro Manila (CNN Philippines, August 12) — President Rodrigo Duterte on Friday said his hardline campaign against illegal drugs faces tough challenges.

Speaking before medical practitioners at the centennial celebration of the Southern Philippines Medical Center in Davao City, Duterte said even the United States could not control its drug problem.

"Hindi makaya nga ng iba, tayo pa kaya? Iyong drugs na iyan (Others can't do it. How can we? Those drugs), we can't control it," Duterte said.

He said having a long coastline to watch over and thousands of islands to guard make it difficult to prevent the entry of illegal drugs.

"We do not have the equipment, kulang man (It's not enough). And you know the coastline," he added.

When he assumed the presidency in July last year, Duterte promised to end the drug problem in six months – or he would resign.

He later said the deadline was a "miscalculation" because he did not realize then how grave the problem was, saying drugs were even funding terrorist groups.

Also read: Duterte: I underestimated the problem on drugs

Duterte's bloody war on drugs, which government data said has killed over 3,400 suspects in police operations since July, has drawn criticisms and outrage from local and international human rights groups.

These groups claim more than 9,000 have died in the drug war.

CNN Philippines' Ina Andolong and Eimor Santos contributed to this report.