JUBA - More than 165,000 people have fled increasing tensions and conflict in South Sudan in the past three months to seek safety both within the country and across borders, the UN refugee agency (UNHCR) said on Tuesday.

"South Sudan cannot afford yet another crisis. The world's youngest country has received more than one million people who fled the ongoing war in Sudan, while millions of its citizens continue to recover from years of conflict and crisis at home," Mamadou Dian Balde, UNHCR's regional director for the East, Horn of Africa and Great Lakes region, said in a statement.

Political instability and rising hostilities since late February between armed groups have led to fresh clashes, particularly in Upper Nile state, but also other hot spots, devastating lives and damaging essential services.

The UN agency said that some 100,000 people seeking safety in the neighboring countries, such as the Democratic Republic of the Congo (DRC), Ethiopia, Sudan and Uganda, cited insecurity, intercommunal violence and deteriorating humanitarian conditions as the main reasons for flight.

According to the UNHCR, humanitarian access to an estimated 65,000 newly internally displaced people in affected communities remains significantly constrained due to fighting and movement restrictions in Upper Nile state and other areas.

Desperately needed aid, including medicine and health care to tackle an increase in cholera cases, has come to a halt, it said, noting that looming rains are likely to exacerbate the situation, with flooding making transport problematic and expensive.

The UNHCR said it requires $36 million to support up to 343,000 internally displaced people in South Sudan and refugees arriving in neighboring countries over the next six months.

"We reiterate calls for an immediate cessation of hostilities and urge all parties to spare civilians more suffering and find a peaceful solution," Balde stressed.

South Sudan remains one of the largest displacement crises in the region, with more than 2.3 million South Sudanese living as refugees in the DRC, Ethiopia, Kenya, Uganda and Sudan, the UNHCR said.