WASHINGTON -- President Barack Obama is warning that the United States may levy sanctions on individuals and entities involved in stoking violence and instability in South Sudan.

Obama signed an executive order Thursday clearing the way for possible visa bans and asset freezes. Officials said the move reflected White House frustration with the lack of progress in ending the violent clashes in South Sudan that broke out more than three months ago.

"Those who threaten the peace, security or stability of South Sudan, obstruct the peace process, target U.N. peacekeepers or are responsible for human rights abuses and atrocities will not have a friend in the United States and run the risk of sanctions," the White House said in a statement.

While no individuals or entities were actually sanctioned Thursday, the executive order is necessary for the U.S. to take that step. Officials said the European Union, Britain, Norway and the United Nations Security Council are also in the process of considering similar actions.

The massive violence in South Sudan erupted in December after a dispute among the country's presidential guards. That dispute soon pitted backers of South Sudan's president against the former vice-president, who now commands the loyalty of a large number of rebel troops who control significant parts of the country.

The politically fueled ethnic violence has continued despite a Jan. 23 cease-fire agreement.

The White House called on both sides to end to the violence, saying there is "no room for excuses or delay."

South Sudan peacefully broke away from Sudan in 2011 after more than 20 years of civil war but had lingering internal grievances that were never addressed.