Kerry is expected to expand assistance on removing unexploded ordnance left in Laos by the United States during the Vietnam War.
In Cambodia, the US diplomat plans to meet government, opposition and civil society members amid "fraught" relations between the ruling and opposition parties.
Kerry will end the regional diplomatic tour with a visit to China on January 27.
"The continuing tensions and problematic behavior by China in the South China Sea is very much on the Secretary’s mind and something that he will certainly discuss in depth," a senior State Department official briefed reporters.
State Department spokesman John Kirby said last week Kerry planned to address North Korea's nuclear program alongside other global, regional and bilateral issues with counterparts in Beijing.
North Korea claimed to have tested a hydrogen bomb earlier this month. However, outside experts said the explosion resembled three earlier tests of a much smaller atomic device.
