The Norwegian People's Aid agency said the men were staff members who were working with the government to develop a database of unexploded bombs from the war.
The Royal Solomon Islands Police Force said the men died Sunday in the bomb blast at the office of their aid project, located in a residential part of the capital, Honiara.
Police said they are still investigating but believe the men had several unexploded bombs at the office and may have been carrying out work to disarm them.
“We are concerned that they decided to conduct explosive ordnance disposal operations within a residential area,” Inspector Clifford Tunuki said in a statement, adding that police later removed other bombs from the site.
Police said they have a close working relationship with the agency.
The city is located on Guadalcanal, an island that was the site of fierce battles between Japanese and U.S. troops and remains littered with unexploded bombs.
“We are devastated by what has happened, and for the loss of two good colleagues,” the head of the Norwegian agency, Henriette Killi Westhrin, said in a statement.
The agency said it has halted its work in the Solomon Islands and is helping police with their investigation. It said the investigation needs to be completed before it reaches any conclusions about what happened.
Authorities have been clearing unexploded bombs ahead of the 2023 Pacific Games, which the Solomon Islands is hosting.
Located northeast of Australia, the Solomon Islands is home to about 600,000 people.