Military and political opposition forces in Aleppo on Sunday rejected UN envoy Staffan de Mistura’s proposal of a temporary ceasefire in the northern Syrian city.
The church has been used as a place of refuge for Assyrian Christians fleeing the chaos of Iraq after the 2003 US-led invasion of that country.
His visit coincided with a mass of solidarity with the scores of Syrian Assyrians kidnapped by Daesh militants in Hassakeh province of northeast Syria.
Last week, Daesh kidnapped 220 Assyrians in the Tal Tamr area where the extremist Islamist group has seized control of 10 Christian villages, according to the Syrian Observatory for Human Rights.
Almost 5,000 people have since fled to Kurdish- and government-controlled areas.