Ethiopian Airlines Group, Africa’s biggest carrier, suspended flights to Eritrea in the latest sign of deteriorating relations with neighboring Ethiopia.

The halt, which is effective from Tuesday, is the result of “very difficult operating conditions it has encountered in Eritrea that are beyond its control,” the state-owned company said in a statement posted on X. It didn’t provide further information.

Ethiopia and Eritrea have a history of adversarial relations. They fought a three-decade war that resulted in Eritrea becoming an independent nation in 1991, depriving Ethiopia of direct access to the sea. Ethiopian Prime Minister Abiy Ahmed signed a peace deal with Eritrean President Isaias Afwerki in 2018, but ties have since been strained Eritrea’s backing of an anti-Abiy militia in Ethiopia.

Addis Ababa’s quest to secure a port in the Gulf of Aden has also heightened tensions in the region. In January, Abiy unveiled a proposal to secure access to a port in Somaliland — a breakaway region in Somalia — in return for a stake in Ethiopian Airlines. Ethiopia has also said it will consider recognising Somaliland as an independent nation, triggering a war of words with Somalia.

Ethiopian Airlines resumed flights to Eritrea in 2018, after an absence of two decades.