At least 20 people were killed and nearly 300 others injured by an explosion at a crowded gas station in Nagorno-Karabakh as thousands of people rushed to flee the cross into Armenia, separatist authorities in the region said on Tuesday.

More than 13,500 people—about 12 per cent of the region’s population—have fled across the border since Azerbaijan’s swift military operation to fully reclaim the breakaway region after three decades of separatist rule, Armenia’s government said on Tuesday morning.