The UN envoy for South Sudan says that after years of conflict, fighting in the world's newest nation "has diminished greatly" since September's peace agreement -- and so has political fighting.

David Shearer said at a news conference Tuesday that he is encouraged by "a number of positive things:" opposition members once at war now in the capital Juba participating in the peace process, more than 15 "peace meetings" across the country, and civilians in UN protected sites starting to return home.

On the less positive side, Shearer said the UN peacekeeping mission he heads is concerned "that the momentum of the peace agreement and the peace talks might slow."

South Sudan plunged into ethnic violence in December 2013 and the five-year civil war has killed almost 400,000 people.