Many fled Rwanda to escape reprisals for mass killings of Tutsi civilians.
The victory ended a genocide by Hutu against Tutsi civilians.
Many of the Hutu refugees had played a part in a massacre of Tutsi civilians in which an estimated half million people died.
Before the coup, the armed Hutu bands knocked down power lines and massacred Tutsi civilians in northern villages.
Aid workers say the militiamen are preventing Tutsi civilians from being rescued from the camps, churches and hotels where they have sought protection.
Hutu guerrillas have stepped up a terrorist campaign against Tutsi civilians in the countryside.
Hutu hard-liners seized control of the country that day and gave the militia the go-ahead to begin killing Tutsi civilians.
On about 13 April 1994, an attack was launched against the Tutsi civilians seeking refuge at Musha Church.
Many Tutsi civilians were killed in the revolution, which was the nation's first ethnically-based conflict, while others fled to semi-permanent refugee settlements in neighboring countries.
Many of them fear retribution for mass killings of Tutsi civilians in 1994.