A South Sudanese military official says fighting has resumed in South Sudan after rebel forces attacked the capital of the oil-producing state of Upper Nile.

South Sudanese military spokesman Col. Philip Aguer said that fighting broke out early Tuesday in Malakal, which once was in rebel hands but is now controlled by government troops.

Although the country's warring factions signed a ceasefire on Jan. 23, both sides have repeatedly accused each other of violating that agreement.

Thousands of people have been killed and more than 800,000 displaced by violence since mid-December, when a fight broke out among presidential guards in the capital, Juba, before spreading out across the country.

Some of the fighting has been along ethnic lines.