Antonio Guterres' statement on Wednesday came after a call with African Union envoy Olusegun Obasanjo following the envoy's latest visit to Addis Ababa and the capital of Ethiopia's embattled Tigray region.

Guterres said Obasanjo ``expressed optimism that there is now a real opportunity for political and diplomatic resolution of the conflict.'' His statement did not describe efforts by Ethiopia's government and the rival Tigray forces, and Obasanjo's spokesman didn't immediately respond to questions.

A new US envoy for the Horn of Africa, Ambassador David Satterfield, is set to meet with Ethiopian officials on Thursday.

Ethiopia's war has killed an estimated tens of thousands of people and displaced millions. The United States says some 900,000 people in Tigray, which has been under an Ethiopian government blockade since late June, face famine conditions.

The World Health Organization says medical supplies have not been allowed into the region of some 6 million people.

Despite his mention of optimism, the UN chief also warned that ``ongoing military operations in some parts of Ethiopia remain a challenge to the peace process and sour the confidence-building measures that we hope are being taken by all parties in the conflict.''

Other combatants include soldiers from neighboring Eritrea who are allied with Ethiopian forces and blamed by witnesses for some of the worst atrocities in the war, as well as fighters from Ethiopia's Amhara region who now occupy western Tigray.

Guterres called on all parties ``to move rapidly towards cessation of hostilities,'' and he said the UN watches the African Union-led mediation efforts with great hope.

The Tigray forces withdrew into their region last month after a drone-assisted military offensive halted their approach to Ethiopia's capital. Ethiopian forces said they wouldn't pursue them further into the region, which some in the international community saw as an opening for mediation efforts.

But several drone strikes have killed scores civilians in Tigray in recent weeks, and Ethiopia's government has not answered questions from The Associated Press about them.