UN Secretary-General Ban Ki-moon on Sunday condemned reported "threats made against UN personnel" in South Sudan, urging all parties to the ongoing conflict in the country to "respect the sanctity" of UN bases where civilians are seeking shelter.

"The secretary-general is alarmed at the attempt today by senior members of the government of South Sudan and South Sudan army to force entry into the protection of civilians site at the compound of the United Nations Mission in South Sudan (UNMISS) in Bor," said a statement issued here by Ban's spokesperson.

UNMISS has been providing protection for nearly 70,000 civilians at its bases, including in Bor in Jonglei state, since conflict erupted in the world's youngest country just over a month ago.

According to the statement, Ban is particularly disturbed that UN staff were threatened by South Sudan military when they refused to allow armed soldiers to accompany civilians to visit the UNMISS protection site.

"The secretary-general condemns the threats made against UN personnel and demands that all parties to the conflict respect the sanctity of UNMISS protection sites," said the statement.

It added that Sunday's incident is just one of a growing number of violations of the Status of Forces Agreement, making it increasingly difficult for UNMISS to implement its mandate and dangerous for UN staff working in South Sudan.

Thousands of civilians have been killed, brutally abused and left homeless in just over a month of conflict in South Sudan, the statement noted.

"The secretary-general calls on the parties and their respective leaders to do far more to ensure that fighters under their command protect civilians and respect international humanitarian law," the statement said. "They should also immediately cease hostilities, which have had such a devastating impact on their young country."

South Sudan army said Saturday it recaptured the strategic town of Bor which was held by rebels loyal to former vice-President Riek Machar,

Since mid-December, South Sudan has witnessed clashes between two military factions, one descending from the Dinka tribe, to which South Sudan President Salva Kiir Mayardit belongs, and the other descending from the Nuer tribe, to which Machar belongs.

The clashes have left more than 1,000 people dead and nearly 500,000 civilians displaced, according to latest UN figures. More than 86,000 South Sudanese have crossed into neighboring countries since the conflict started.