SEOUL, South Korea — South Korea has been forced to repeatedly shut down runways at the two main airports for the capital, Seoul, since June due to disruption from trash-carrying balloons launched by North Korea, a South Korean lawmaker said Wednesday, citing aviation data.

On 20 different days since June 1, all or some runways at Incheon and Gimpo airports were closed for landings or takeoffs, or both, when balloons were detected in the vicinity, Democratic Party lawmaker Yang Bu-nam said…