The United States on Saturday expressed concern over reported violations of a shaky ceasefire agreement between South Sudan's government and rebel forces and urged the removal of foreign fighters engaged in the conflict.
Thousands of people have been killed and more than half a million have fled their homes since fighting erupted in December in a conflict that has brought oil-producing South Sudan to the brink of civil war.
State Department spokeswoman Jen Psaki said the United States is "deeply concerned by reports of violations by both the government of South Sudan and anti-government forces" of the ceasefire deal.
"We urge the redeployment or phased withdrawal of foreign forces invited by either side, and warn of the serious consequences which could result from any regionalization of this conflict," Psaki said in a statement.
President Salva Kiir's government and rebels loyal to his fired deputy, Riek Machar, agreed to the ceasefire on Jan. 23, but both sides have since accused each other of violations.
Regional and world powers worry about the potential for a spillover of violence in an already volatile part of Africa. South Sudan declared independence from Sudan in 2011.
The rebels have accused government SPLA forces and fighters from the Sudanese Justice and Equality Movement - a rebel group from north of the border - of razing Machar's hometown, massacring women and children as they fled. The government also accuses the rebels of flouting the ceasefire.
An advance team sent by east African nations to monitor the ceasefire arrived in South Sudan last Sunday. Violence erupted in the capital, Juba, in December before spreading across the world's newest nation.
Psaki said the United States welcomed the arrival in Juba of the first component of the monitoring team, adding that "we strongly urge the government of South Sudan to facilitate (the team's) important work, which will provide both sides with a mechanism to report any breaches of the agreement."
Psaki reiterated a U.S. request for the government's release of the last four of a group of 11 detainees held on suspicion of trying to stage a coup.
"The expeditious release and transfer of all of the detainees would reduce tension and build confidence in an inclusive reconciliation process," Psaki added.