WASHINGTON, Jan. 5 (Xinhua) -- The United States on Saturday urged the warring parties in South Sudan to achieve "rapid, tangible" progress in ending their conflicts through direct talks, stressing there is no military solution.

The appeal from State Department spokeswoman Marie Harf came as forces loyal to South Sudan President Salva Kiir and his former deputy Riek Machar were set to start talks on Sunday in Addis Ababa, capital of Ethiopia.

"The parties must use these talks to make rapid, tangible progress on a cessation of hostilities, humanitarian access, and the status of political detainees," Harf said in a statement.

"There can be no military solution to this conflict," she added. "Forging a durable and lasting peace depends on resolving the underlying political causes of the conflict."

About 1,000 people have been killed and up to 190,000 others displaced since deadly clashes erupted between the warring parties in Juba, South Sudan's capital, on Dec. 15 and spilled over to other parts of the country.

U.S. special envoy Donald Booth was in Addis Ababa for the talks, sponsored by the regional Intergovernmental Authority on Development.