Sudan's newly-created sovereign council formally declared a state of emergency in the city of Port Sudan on Sunday, following tribal clashes that police say have killed at least 16 people.

The acting governor and the head of the national security service for the eastern Red Sea state, of which Port Sudan is the capital, were both dismissed, said Brigadier Altahir Abuhaja, spokesman for the sovereign council.

This comes at a delicate time for Sudan, following the signing of a power-sharing agreement earlier this month.

The joint military-civilian sovereign council was sworn in last week, as was Prime Minister Abdalla Hamdok, who is set to form a government later this week.

Clashes between members of the Beni Amer and Nuba tribes, which have flared up in the past, were re-ignited on Wednesday and continued into Saturday morning, a police statement said.

Eyewitnesses told Reuters they heard and saw gunfire in the Port Sudan neighborhoods where both tribes live.

Port Sudan is Sudan's main sea gateway, and is used by South Sudan to export oil.

"The relevant authorities have observed the use of firearms in the conflict for the first time, which reveals the existence of external and internal interference to fuel the conflict and spread it to other areas," Abuhaja said.

Security services were placed on high readiness in order to quell any escalation, and an investigative committee has been formed, he added.

The police statement said reinforcements had been sent to the area.

"The transitional sovereign council emphasizes the neutrality of the military and security services... Anyone who is shown to be biased to either side because of affiliation or support will be dealt with decisively," Abuhaja said.

Two members of the sovereign council had visited Port Sudan on Thursday and met with tribal leaders in an attempt to bring an end to the fighting.

According to the power-sharing agreement, the sovereign council declares a state of emergency following a request from the cabinet, which is not yet in existence. The state of emergency must then be approved by the legislature within 15 days, according to the agreement, although the legislature is yet to be formed.