The US leader, standing alongside his South Korean counterpart Moon Jae-In, reiterated he was prepared to use the full range of American military might in order to halt Pyongyang's march towards becoming a full-fledged nuclear power.
But he added: "It makes sense for North Korea to come to the table to make a deal that is good for the people of North Korea and the people of the world."
"I think we are making a lot of progress," he said, adding that Chinese President Xi Jinping -- whom he has often claimed holds the key to disarming the North -- has been "very, very helpful".
After a relaxed few days in Tokyo, Seoul is a more complicated stop for the mercurial US president.
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Trump's relationship with the liberal-leaning Moon has been cool, and the former real estate magnate has railed at South Korean moves to engage its neighbour -- something he has previously labelled "appeasement".
But he began his diplomatic day vowing to "figure it all out" with "fine gentleman" Moon, despite their differences on the nuclear-armed North.
Trump arrived from Japan, where he secured Tokyo's full support for Washington's stance that "all options are on the table" regarding Pyongyang, and declaring its nuclear ambitions "a threat to the civilised world and international peace and stability".
He enjoyed three days of near-bromance with Prime Minister Shinzo Abe, calling him "wonderful" after a round of golf and describing US-Japan ties as "really extraordinary".
But at Camp Humphreys on Tuesday, where US forces stationed in the country have moved their headquarters from downtown Seoul, he and Moon sought a rapprochement.
And Moon -- whose parents were evacuated from the North on a US ship during the Korean War -- was abundant in his praise for the United States.
"They say one knows a true friend when one is in need," he told Trump. "The United States is a true friend who has been with us and has bled with us in our time of need."
South Korea is rolling out the red carpet for Trump as it seeks messages of assurance about the alliance and US resolve.