CLARK, Philippines (AP) — U.S. Defense Secretary Jim Mattis, paving the way for a visit next month by President Donald Trump, congratulated the Philippine army for its successes against militants in the southern city of Marawi.

The U.S. and the Philippines are decades-old treaty allies, but the relationship has been rocky in recent years. One point of contention under President Barack Obama was government-sanctioned killings as part of President Rodrigo Duterte's crackdown on drug suspects. President Donald Trump has praised Duterte's attacks on drug suspects.

Mattis arrived early Monday at an airbase that once of the home of U.S. air forces known as Clark field. He will be attending meetings with counterparts from 10 Southeast Asian nations. A key topic is expected to be North Korea and its accelerating drive to develop a full arsenal of nuclear weapons, including missiles capable of strike the United States.

Mattis was scheduled later Monday to hold trilateral talks with his counterparts from South Korea and Japan as part of a Trump administration effort to present a united front on North Korea and to prepare for the possibility of conflict.

In brief remarks to reporters flying with him from Washington, Mattis praised the Philippine military for its counterterrorism efforts in Marawi, which had been controlled by Islamic militants.

"The Philippine military has sent a very necessary message to the terrorists," Mattis said.

The Philippine military said on Sunday that its troops were battling a final group of about 30 pro-Islamic State group militants as a nearly five-month siege neared its end in Marawai.

A gradual withdrawal of forces was underway with the easing of the fighting, which has left at least 1,131 people dead, including 919 militants and 165 soldiers and policemen.