Eritrea has been helping neighboring Ethiopia fight off rebel troops by mobilizing military reservists to strengthen the army.
Security forces have started stopping people in several places to determine whether they are exempt from military conscription.
Witnesses report seeing groups of men sobbing as they said goodbye to their families.
Reservists up to the age of 55 have been called up, they said.
Eritrea has compulsory, decades-long military service, which has been widely criticized by human-rights groups, but analysts say the latest mobilization efforts are linked to the civil war in northern Ethiopia – a conflict that recently flared up again after five months of relative peace.
Witnesses told BBC News Tigrinya that mobilization notices were distributed on Thursday in the capital, the second-largest city, Keren, the western town of Tessenai, and other areas.
They called on reservists to report to their respective head offices, while also advising that they should carry their own supplies, including blankets and water containers.
Mothers, children and wives were crying as they bid farewell to their sons, fathers, brothers, and husbands, sources told the BBC.
Those who do not heed the call-up have been warned of severe consequences, but some are reportedly ignoring it.
Eritrea has been fighting alongside Ethiopia’s central government troops since the civil war broke out in Tigray in late 2020.
Several human rights organisations have accused Eritrean soldiers of committing atrocities in Ethiopia, but these claims have been denied by Eritrean officials.
The US has imposed sanctions on the Eritrean Defence Forces and the ruling PFDJ party in response to their involvement in the conflict.
President Isaias Afwerki has ruled Eritrea since the country broke away from Ethiopia in 1993, but between 1998-2000 the two nations fought a brutal and costly war over a contested border area.
A 20-year military stalemate ensued until Abiy Ahmed became Ethiopia’s prime minister in 2018. The peace deal won Mr Abiy the Nobel Peace Prize a year later.
