In an interview with "Fox & Friends'" Steve Doocey on the White House lawn, Trump said that he asked North Korean leader Kim Jong Un during their summit talks on Tuesday to return the remains of US troops killed in the country.
In a statement, Pentagon spokesperson Dana White said Mattis and Song discussed how the two nations are working together to "fulfil the President's guidance on US-South Korean combined military exercises".
The message was passed to the president of the North Korean Supreme People's Assembly, Kim Yong Nam, visiting Moscow as the World Cup kicks off in the country. The Washington Post notes the importance of the inclusion of this awkward moment in the documentary, which was aired across North Korea. After reassuring American allies Japan and South Korea this morning in Seoul, he flew to Beijing, where he said the US would consider making a call to lift economic sanctions on the North.
Mr Trump's nominee as next ambassador to South Korea, Harry Harris - previously a supporter of the drills - has said that "major exercises" should be paused to allow time to test Pyongyang's commitment about dialogue.
"He is the strong head", Trump said of Kim during a surprise appearance Friday on Fox News. Say an American solider was 18 when he was sent to North Korea in the war's final year, 1953 - he would have been 80 in 2015; if his parents had given birth to him when they were 18, they would have been 98 in 2015.
He told reporters that "one should heavily discount some things that are written in other places - including from some of your colleagues!"
"He speaks and people sit up at attention", Trump said.
But following his talks with Kim Jong-un in Singapore, Mr Trump described the drills as "very provocative" - contradicting previous USA administrations' insistence that the drills are purely defensive - and said he was ending them.
"You know you call people sometimes killers, he is a killer".
North Korea's news doesn't just give its citizens state-approved information.
Mr Kim previously praised Mr Trump for taking the initiative with North Korea where previous presidents had not.
"We save a fortune by not doing war games, as long as we are negotiating in good faith - which both sides are!" he wrote on Twitter.