MANILA - President Rodrigo Duterte on Thursday warned of a possible retaliation by terrorist groups in the wake of the liberation of Marawi City from Islamic State-inspired fighters.

“The military has been mouthing it and the police, several times, that we prepare for retaliation,” Duterte said in a speech in Manila.

“We know and I know that it is coming. When? We really do not know.”

Duterte last Tuesday declared that Marawi has been finally liberated from terrorists following the killing of the siege's leaders Isnilon Hapilon and Omar Maute.

Both military officials and security analysts, however, agree that state forces must not become complacent and prepare for a possible retaliatory attack from the terrorists.

The killing of the two top terrorist leaders marked a major development in the nearly 5-month siege that has left the predominantly Muslim city in ruins.

The military has also expressed confidence that another high-value terrorist, Malaysian professor Mahmud bin Ahmad, was killed in a Wednesday assault by the military.

Over 1,000 people, mostly terrorists, have died since clashes erupted in the city. At least 400,000 residents in Marawi City and outlying areas were also forced to evacuate.

The siege prompted President Duterte to place the entire Mindanao under martial law.

The recapturing of Marawi City by state forces marks another big blow to the Islamic State, which had been seeking to establish a new front in Southeast Asia amid heavy losses in the Middle East.