Islamist militants attacked a convoy taking supplies to a town in northern Burkina Faso, with eleven soldiers found dead and about 50 civilians were reported missing.
The constitution has been suspended and the transitional charter dissolved, borders are closed indefinitely and all political and civil society activities are suspended.
The United Nations condemned the attack that "claimed many victims" in a statement on Monday and called on authorities to bring perpetrators to justice.
The nun was named as Suellen Tennyson.
The country had already been suspended from the West African regional bloc, the Economic Community of West African States.
The broadcast came after two days of confusion and fear in Ouagadougou, the capital, where shooting erupted at army camps on Sunday.
Mutinying soldiers demanded more support for their fight against Islamist militants and protesters ransacked the headquarters of President Roch Kabore's political party.
According to the UN, nearly 4,000 people have been murdered in related terrorist attacks throughout Burkina Faso and the surrounding territories - including neighboring countries Mali and Niger.