The regime of Bashar al-Assad in Syria must come to an end, U.S. President Barack Obama told the UN General Assembly on Tuesday.

In Syria, the future should “not belong to a dictator who massacres his own people,” Obama told UN delegates, referring to Assad.

The United States and its allies have repeatedly insisted that Assad must step down from power, though Russia has warned that taking sides in the type of civil war ravaging Syria can lead to dangerous unintended consequences.

Obama on Tuesday again expressed support for the jumbled coalition of opposition groups seeking to depose Assad.