A senior Roman Catholic Church leader in South Sudan has condemned the government there for its role in violence last weekend.

Apostolic Administrator Rocco Taban unleashed a furious broadside in a sermon on Sunday, according to the Radio Tamazuj news service.

He spoke after the country's second city Wau descended into violence which culminated in fighting on Saturday between armed opposition and government soldiers. Ethnic tensions in the city, which is inhabited by people from many tribes, are believed to have contributed to the violence, which saw thousands displaced and dozens killed.

In a sermon at St Joseph's Catholic Church in the capital, Juba, Taban alleged government complicity in the violence and criticised it for removing the recently appointed governor.

"More than 100,000 people are in the bush being displaced by their own government. This is the country we have chosen. This is the country we have voted for its independence so that our country displaces us. Our own country. We are ruled really by monkeys. We are ruled by monkeys. We have to be very clear: We are ruled by monkeys," said Rocco.

He continued: "And the governor who was protecting people in Wau, who was loved by the people in Wau, General Elias Waya [was] removed by the presidential decree and being replaced by [a] madman."

The new governor, Andrea Mayar, was impeached as speaker of the legislative assembly in Wau last year. He was appointed governor on Friday hours before serious fighting erupted.

Taban said: "Do we love our country? Do we love this nation? And so far the President of the Republic did not say even a word. In Australia three people were killed three days ago. The Prime Minister came out three times a day to make a statement. Because of three Australians."

He continued: "They are eating and drinking and sleeping. Devils! These are devils! We are ruled by devils. And we are very sorry for them," he said.

The priest concluded, "We don't want to call fire on them, because we will go against Christ. But they have to understand that they are devils. And they are devils. And they are ruling us with evil powers. They are criminals."

South Sudan has been riven with political and inter-communal strife since its independence from Sudan, achieved after a decades-long, bloody struggle involving a fractious coalition of different factions. Most recently conflict broke out between President Salva Kiir and his former deputy Riek Machar. The two-year struggle came to a formal end in April with the formation of a new unity government, but tensions remain. 

Government forces – the Sudan People's Liberation Army – have been accused of atrocities and of acting as a terrorist militia, including in Wau, according to Human Rights Watch.

UN Secretary-General Ban Ki-moon said he was deeply concerned about the violence. "The Secretary-General calls on all fighting forces to immediately suspend the hostilities, provide access to the United Nations Mission in South Sudan and cooperate with humanitarian partners to facilitate the delivery of assistance," a spokesman said. "He urges all parties to agree to dialogue to resolve their political disputes."