Government fighters attacked positions held by troops on Saturday, an indication that a fragile cease-fire that took effect on Friday may be beginning to fray.
The information minister Michael Makeur Lueth told reporters that opposition fighters were continuing attacks on government forces. He said the government security forces would defend themselves if the attacks continued.
The information minister did not specify where Saturday's unrest was taking place.
His comments come a day after an opposition fighter said President Salva Kiir's forces attacked rebel positions in Unity and Jonglei states. General Lul Ruai Koang said government forces were aided by rebels from Sudan's Darfur region and Ugandan forces. However, on Twitter, South Sudan military spokesman Philip Aguer said he had received no reports of fighting.
Representatives for the government and the opposition signed a cease-fire agreement in Ethiopia on Thursday, in a bid to end weeks of fighting that is believed to have left over 1,000 people dead and an estimated half-million displaced.
The unrest began in mid-December after President Kiir accused his former vice president, Riek Machar, of attempting a coup -- a charge Machar has denied.
U.N. humanitarian chief Valerie Amos begins a three-day trip to South Sudan on Monday. The U.N. says she will meet with government officials and aid groups in an effort to draw attention to the "humanitarian consequences" of the country's unrest.