OTTAWA—The G7 says it will ramp up its efforts to hold Belarus accountable for arresting a dissident journalist on board an intercepted jetliner, though additional penalties have yet to be nailed down. In a statement Thursday, the countries’ foreign ministers along with a European Union representative said they will impose “further sanctions as appropriate,” condemning the act as an attack on press freedom and civil aviation rules. The EU has already moved to ban Belarusian airlines from its skies, advised EU carriers to steer clear of flights over Belarus and pledged further economic sanctions. On Sunday, Belarusian air traffic controllers diverted a Ryanair flight between Greece and Lithuania to Belarus’s capital, Minsk, claiming there was a bomb threat. On the ground, authorities detained journalist Roman Protasevich and his girlfriend Sofia Sapega, who both later appeared in videos under apparent duress. The G7 is calling for immediate action from the International …