The United States says it has pulled out of an international economic conference on Sudan and South Sudan because of “ongoing conflicts in Sudan.”

In a statement Tuesday, the U.S. State Department said it is “not clear” the conference “'can be effective” at this time.

The two-day conference was to begin in Istanbul on March 23.

Sudan's armed forces have been battling rebels along the country's southern border since the middle of last year. Khartoum says the rebels are aligned with South Sudan, which declared independence in July.

South Sudan denies supporting the rebels.

Witnesses have also accused Sudan of carrying out air strikes against civilians in Southern Kordofan and Blue Nile states. Khartoum has denied those charges.

The State Department said the conference will be rescheduled and that Washington will work with Turkey, Norway and other partners that ensure both Sudans are stable and prosperous.