First lady Melania Trump, the president's daughter Ivanka Trump and son-in-law Jared Kushner accompanied him.
Duterte declared martial rule for 60 days in the entire southern Mindanao region to try to crush Muslim extremists who've occupied parts of a city.
Salman Abedi, who investigators say was responsible for the carnage, had ties to al Qaeda and had received terrorist training abroad, a U.S. intelligence official told NBC News.
Ariana Grande's fans are predominantly teens and young girls, and many had gone to the venue for a night of fun that turned into a scene of carnage.
President Donald Trump is expected to retain attorney Marc Kasowitz in matters related to the Russia investigation, sources say.