There are more than 30,000 people on UN bases in the capital Juba, 18,000 in Malakal in Upper Nile State and around 38,000 in the oil hub of Bentiu, said spokesman Stephane Dujarric yesterday.
"That's the largest figure recorded since the beginning of the crisis in mid-December," Dujarric told reporters.
The UN Mission in South Sudan says most new sites for internally displaced people have been or are very close to completion.
The UN peacekeeping force has been bolstered by the arrival of 800 Rwandan soldiers, most of them deployed to Malakal.
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Around 300 Ghanians have gone to Bentiu and two Ethiopian battalions of 1,700 are expected in the coming days.
In December, the UN Security Council voted to double the world body's peacekeeping mission in South Sudan by sending an extra 6,000 blue helmets, essentially diverted from other missions.
The conflict in the world's youngest and one of its most poor countries has killed thousands and forced more than 1.5 million to flee their homes.
Both the government of President Salva Kiir and rebels loyal to former vice president Riek Machar currently refuse to restart talks aimed at ending the six-month conflict.