"Right now, I think there is a lot of reasons for optimism that the negotiations will be fruitful," Mattis told reporters.
The announcement comes amid a planned meeting set later this year between President Trump and the North Korean dictator.
Promises of North Korea's good behavior in return for concessions from the U.S. have not worked in the past.
Chinese President Xi Jinping Thursday stressed the "urgent" need to build a powerful navy during a surprise visit.
The USS Mustin conducted maneuvers within 12 nautical miles of Mischief Reef -- drawing a rebuke from China.
After decades of relative calm across the Pacific region, Wake Island is taking on a renewed strategic importance.
The White House put tough conditions on the proposed summit with North Korea.
President Donald Trump agreed to hold face-to-face peace talks with North Korea's Kim Jong Un.
U.S. officials say the port call is a sign of the U.S. commitment to the region and U.S.-Vietnam ties.
The agreement brightens prospects for a dialogue between North Korea and the U.S.