Tens of thousands of refugees from Myanmar have fled north across the Chinese border in recent weeks, driven by escalating fighting between Myanmar’s military and the Kachin Independence Army (KIA), according to aid workers in China’s Yunnan province.

The growing wave of refugees highlights a decades-old conflict between ethnic Kachin rebels and Myanmar’s army that diplomats see as a blight on efforts by president Thein Sein’s nominally civilian government to bring the country out of international isolation.

Both the US and European Union have set the resolution of conflict with ethnic militias as a key condition for lifting sanctions against Myanmar. For decades, the conflict has driven hundreds of thousands of villagers from their homes amid charges by human rights groups of military abuses including rape, forced labour and torture.