EU foreign policy chief Catherine Ashton is sending an envoy to help seek a political solution to ethnic bloodletting in South Sudan and to liaise with neighbouring countries, the European Commission said on Wednesday.

"It is essential that all political leaders commit immediately to a political dialogue to resolve their differences," Maja Kocijancic, a spokeswoman for Ashton, said.

In an emailed statement, she said Ashton had asked EU special representative Alex Rondos to travel to the region immediately and to liaise directly with concerned countries and organisations on the ground.

The U.N. Security Council on Tuesday approved plans to almost double the number of peacekeepers in South Sudan in response to fears of a worsening conflict there.