The violence in Tigray, which has spilled over into neighbouring regions and drawn in the Eritrean military, has killed thousands of civilians, uprooted millions and left hundreds of thousands now facing possible famine.
The conflict stems from grievances rooted in periods of Ethiopia's turbulent past when particular regional power blocs held sway over the country as a whole, and in tensions over the balance of power between the regions and the central state.
Shire is about 140km northwest of Tigray's regional capital Mekelle and hosts tens of thousands of people displaced from other areas by the conflict.
Just as news of Shire's capture was emerging, United Nations Secretary General Antonio Guterres was calling for an immediate end to hostilities in Tigray and a return to peace talks sponsored by the African Union.
Guterres told reporters the UN was ready to support the bloc in every possible way to end the Ethiopian people's "nightmare".
The European Union said the joint offensive by Ethiopian and Eritrean forces should stop immediately and the Eritreans should withdraw from Ethiopian territory.
It also urged Tigray forces - led by the Tigray People's Liberation Front (TPLF) - to refrain from any further military operations.
Spokespersons for the Ethiopian government and army, for the Eritrean government and for the Tigray forces did not respond to requests for comment on events in Shire.
In a post on Twitter, the Ethiopian foreign affairs ministry referred to "areas liberated and controlled" by the country's army, saying the government was ready to ensure humanitarian access and ensure the safety of humanitarian workers.
It did not specify which areas it was referring to.
An aid worker from the International Rescue Committee was among three people killed during an air strike on Shire on Friday.
On Sunday, Samantha Power, head of US development agency USAID, said there was a significant risk of attacks on civilians if the Ethiopian and Eritrean armies took control of camps sheltering displaced civilians.
In September, a UN human rights commission said it had reasonable grounds to believe that war crimes had been committed by forces from both sides of the conflict, which have all denied perpetrating abuses.
Earlier on Monday, the Ethiopian government said it aimed to seize airports and other infrastructure currently under the control of the Tigray forces, even as it stated it was committed to a peaceful resolution of the conflict through peace talks.
The Tigray authorities said on Sunday their forces would abide by an immediate truce and said a "humanitarian catastrophe" was unfolding.
Both sides blame each other for breaking a ceasefire in August that had lasted since March.
Peace talks proposed for earlier this month in South Africa were delayed with no new date announced.
