The African Union’s special envoy for the Horn of Africa, Olusegun Obasanjo, remains hopeful that dialogue can end Ethiopia’s year-long war, but warned in a statement released Sunday that “such talks cannot deliver” without an immediate ceasefire.

The former Nigerian president is leading an international push to end a conflict that has cost thousands of lives and displaced two million people, as fears of a rebel march on Ethiopia’s capital Addis Ababa prompt a flurry of diplomatic activity.

Obasanjo, who left Ethiopia on Thursday after meetings with Prime Minister Abiy Ahmed and the leadership of the Tigray People’s Liberation Front rebel group, said he was “optimistic that common ground towards a peaceful resolution of the conflict can be secured.”

But with fighting intensifying in recent weeks and the TPLF claiming major territorial gains, he warned that “such talks cannot deliver in an environment of escalated military hostilities.”

“I, therefore, appeal to the leadership of all sides to halt their military offensives. This will allow an opportunity for dialogue to continue to progress.”

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His comments came ahead of a three-nation visit to Africa by US Secretary of State Antony Blinken, who has backed Obasanjo’s efforts at mediation and threatened to impose sanctions on Abiy’s government and the TPLF unless they move forward on talks.

Ethiopia on Thursday laid out conditions for possible talks with the rebels, including a halt to attacks, a TPLF withdrawal from the neighbouring areas of Amhara and Afar, and recognition of the government’s legitimacy.

The TPLF in turn is demanding that aid be let into Tigray, the region where the conflict erupted last year. No assistance has arrived by road since October 18, and 364 trucks are stuck in Afar awaiting authorisation, according to the United Nations.

Abiy sent troops into Tigray last November to topple the TPLF, a move he said came in response to rebel attacks on army camps.

Though the 2019 Nobel Peace laureate vowed a swift victory, by late June the TPLF had retaken most of Tigray before expanding into Amhara and Afar.