"Hostilities in the Tigray region of Ethiopia must end now," UN Secretary General Guetrres said Monday, calling for the "immediate withdrawal and disengagement" of Eritrean forces.
"The situation in Ethiopia is spiraling out of control. Violence and destruction have reached alarming levels," Guterres told reporters at the United Nations.
Ethiopian Prime Minister Abiy Ahmed's government said Monday it was "committed to the peaceful resolution of the conflict through the AU-led peace talks," without addressing the ceasefire call.
But it said it would also pursue "defensive measures" to protect Ethiopia's sovereignty and territorial integrity from internal and external threats.
The Government Communication Service (GCS) said "It is thus imperative that the Government of Ethiopia assumes immediate control of all airports, other federal facilities, and installations in the region."
Reacting to the GCS statement, TPLF spokesman Getachew Reda told AFP in a message: "It's a clear indication that the government and its ally will do everything to carry through their genocidal intent against the people of Tigray."
Meanwhile, civilian casualties have been reported in heavy shelling as Ethiopian and Eritrean troops wage an offensive near Shire, a city of 100,000 people in northwestern Tigray.
US aid chief Samantha Power on Sunday warned "the risk of additional atrocities and loss of life is intensifying" around Shire, and accused Ethiopian and Eritrean forces of indiscriminate attacks.
Britain's minister for Africa, Gillian Keegan, said she was "appalled" by the attack.
Addis Ababa said its army strove to "avoid combat operations within urban areas to prevent civilian casualties" but urged aid workers to "distance themselves from TPLF military assets".
"The Government of Ethiopia deeply regrets any harm that might have been inflicted on civilians, including humanitarian personnel," the GCS said, adding it would investigate such incidents.
On Friday, an aid worker from the International Rescue Committee (IRC) was among three civilians killed in an attack in Shire that also injured others.
The IRC staffer was distributing food to vulnerable civilians including women and children, said the World Food Program (WFP).
"This is the 24th aid worker killed in Tigray since the start of the conflict. Civilians and aid workers must be protected and #NotATarget," Keegan wrote on Twitter.