"Right now, I think there is a lot of reasons for optimism that the negotiations will be fruitful," Mattis told reporters.
President Trump claimed North Korea has agreed to "denuclearization." But that's not the case.
On Friday, the State Department released its annual report on global human rights violations.
Asked this week about the status of the detained citizens, President Trump said their return home remained a priority.
The announcement comes amid a planned meeting set later this year between President Trump and the North Korean dictator.
President Trump said that although he's looking ahead to a historic summit meeting with Kim Jong Un he could still pull out.
President Donald Trump on Wednesday confirmed that his CIA chief secretly met with Kim Jong Un in North Korea.
Promises of North Korea's good behavior in return for concessions from the U.S. have not worked in the past.
North Korea's government says that leader Kim Jong Un is ready to discuss his nuclear weapons program with President Trump.
South Korean media have speculated whether Kim will cross the Military Demarcation Line in a symbolic gesture of peace.