A vigil is being held at an Anglican church in Addis Ababa, for nine Ethiopians still being held captive after their kidnap in the Afar region.
There has been no word on the missing Ethiopians
There has been concern over the safety of the Ethiopians who were taken hostage along with five British embassy workers earlier this month.
Armed bandits seized them, but freed the foreigners to the authorities of neighbouring Eritrea on Tuesday.
Eritrea has denied Ethiopian claims that they were behind the kidnapping.
The Afar region straddles the border of Ethiopia and Eritrea.
Relations between the two countries have been strained since Eritrea gained independence from Ethiopia in 1993 after a 30-year guerrilla war.
The BBC's Amber Henshaw in the capital, Addis Ababa, says Ethiopians and members of the international community turned out in St Matthew's church.
They held a minute's silence and lit candles.
The freed hostages have now arrived back in the UK.
The Afar Revolutionary Democratic Unity Front, an Ethiopian rebel group operating within the region, has been blamed for the kidnapping.
But the Ethiopian foreign ministry has accused Eritrea of master-minding the abduction, fuelling further tensions between the bitter rivals.
Eritrea, which has a border dispute with Ethiopia, has dismissed the accusations.
"These are outrageous allegations with no factual basis," Eritrean presidential spokesman Yemani Gebremeskel told Associated Press news agency.
Ethiopian officials say the hostages may have been marched through its porous border to Eritrea. But is not clear where the Ethiopian captives are being held.
The group were touring the Afar region, one of the hottest, most remote places on earth.
It is believed that Afar tribal elders negotiated with the kidnappers to secure the foreigners' release.