US ambassador to UN evacuated from South Sudan camp amid protests
Haley was meeting with civilians impacted by the South Sudan conflict when several hundred people demonstrating against President Salva Kiir approached the event, according to a spokesman for the US mission to the UN.
Haley's security team deemed it was unsafe and escorted her away.
The UN envoy visited Juba on Wednesday, seeking a solution to a nearly four-year conflict that has created a devastating humanitarian crisis.
She is on a tour that has also taken her to Ethiopia and will include Democratic Republic of Congo.
After meeting with President Salva Kiir, Haley said the US was disappointed with the state of South Sudan, after investing $11 billion (nine billion euros) in the country under Kiir's leadership.
"We are disappointed by what we are seeing, this is not what we thought we were investing in. What we thought we were investing in is a free and fair society where people could be safe, and South Sudan is the opposite of that," Haley told local radio.
"But we are not going to give up on the South Sudanese people, we are here to fight for them, we are here to help, to do whatever we have to to make peace and security become a permanent part of South Sudan," she added.
There was no comment from Kiir after the meeting.
Haley said last month she wanted to salvage a tattered 2015 peace deal that collapsed in July last year, as regional mediators launch a fresh bid to "revitalise" the agreement.
South Sudan won independence in 2011. However, war erupted in December 2013 when Kiir accused his former deputy, Riek Machar, of plotting a coup.
Initially a war pitting ethnic Dinka supporters of Kiir against Machar's Nuer people, the conflict has since metastasised to include different groups and local interests.