In a joint statement, the United States, Britain, Australia, Denmark, Germany and The Netherlands said they were "profoundly concerned" by the shattering of the five-month truce in late August.
"We call on the parties to recognize there is no military solution to the conflict, and we call on the government of Ethiopia and the Tigray regional authorities to participate in African Union-led talks aimed at helping Ethiopia achieve a lasting peace," the statement said.
The Western nations warned of abuses by all sides including Ethiopia, the Tigray People's Liberation Front and Eritrea, which has returned to the conflict to back Ethiopian Prime Minister Abiy Ahmed.
"The resumption of fighting in northern Ethiopia raises a high risk of further human rights violations and abuses," it said, adding that "any durable solution must include accountability for human rights abuses and violations."
The rebels agreed, after prolonged hesitation, to accept mediation by the African Union, which is based in Addis Ababa.
But after the bloc called talks for last weekend in South Africa, former Kenyan president Uhuru Kenyatta, who was to be playing a key role in negotiations, said he could not attend.
The Western nations called for a withdrawal of troops from Eritrea, one of the world's most closed and authoritarian nations.
"All foreign actors should cease actions that fuel this conflict."