North Korea's Kim Myong Gil and Stephen Biegun, the special envoy of US President Donald Trump, are part of the teams at the talks, AFP wrote.
The two were to meet at a heavily guarded venue on an island off Stockholm, several hundred meters from the North Korean Embassy.
"I am encouraged that US and (North Korean) working level delegations are currently in Sweden to hold talks," Swedish Foreign Minister Ann Lindh tweeted.
"Dialogue needed to reach denuclearization and peaceful solution."
Similar-level talks on North Korea's nuclear disarmament were held in Stockholm in March 2018 and then in January this year.
Pyongyang tested what it called a "super-large" rocket on Wednesday just hours after it said it was willing to resume working-level talks with Washington.
Kim Myong Gil said he was "optimistic" about the talks, speaking in Beijing on his way to the Swedish capital.
Washington has been eagerly awaiting a resumption of the dialogue, which has virtually stalled after a Hanoi meeting in late February between Trump and North Korean leader Kim Jong-un.
North Korea said to have entered a new phase in its defense capability with Wednesday's test of a submarine-launched ballistic missile.
The Pentagon said Thursday the missile seems to have been launched from a "sea-based platform" and not a submarine.
Trump has said he sees no problem with a string of short-range rocket tests conducted previously by North Korea, while insisting his personal ties with the North's leader remain good.
Photos carried by Pyongyang's official Rodong Sinmun newspaper showed a black and white missile emerging from the water and appearing to shoot into the sky.
The images also showed a small towing vessel next to the missile, which analysts said indicates the test was conducted from a submersible barge rather than an actual submarine, and that the system was in its early stages.