The gunman, whose identity was still unknown, killed himself in a hotel room after being shot by security officers at the Resorts World Manila entertainment complex, police said.

A second "person of interest" who was in the casino at the time is cooperating with the investigation, police said.

Read: Gunman Torches Philippine Casino Killing 36 People

Pantaleon Alvarez, a speaker of the lower house of Congress and a close ally of President Rodrigo Duterte, said he was not convinced the incident was a criminal case of armed robbery and arson.

"This is a clear example of a 'lone wolf' terrorist attack targeting civilians to inflict maximum loss of life and damage to property, as what has happened in other countries," Alvarez said in a statement.

Islamic State (IS) claimed responsibility for the attack, but that was rejected by Philippines officials, who said it appeared to have been a botched robbery.

Duterte's spokesman, Ernesto Abella, said on Friday there was no proof linking it to a protracted urban battle between government troops and Islamist militants in the country's south, while his security adviser, Hermogenes Esperon, said all the evidence pointed to an attempt to steal casino chips.

"We must draw up a clear and better plan to secure Metro Manila and other urban centers from IS-linked groups that we already know will attempt to kill and maim in pursuit of their jihadist ideology," Alvarez said.

The Philippines has been on heightened alert amid a crisis in the city of Marawi, on the southern island of Mindanao, where troops have been battling Islamist rebels since May 23 and martial law is in place.

REUTERS