Qatar Airways is suing its neighbors in the Gulf over the closure of their airspaces to the Doha-based airline.

The head of the group that owns Qatar’s flagship carrier said the closure by Saudi Arabia and its allies during the 2017 Qatar diplomatic crisis violated international aviation norms and caused unlawful damages.

“The decision by the blockading states to prevent Qatar Airways from operating in their countries and flying over their airspace is a clear breach of civil aviation conventions and several binding agreements they are signatories to,” Qatar Airways Group CEO Akbar Al Baker said in a statement.

In 2017, Saudi Arabia, the United Arab Emirates (UAE), Egypt and Bahrain closed their airspace to flights originating from Qatar. They also closed their land and sea borders with Qatar and severed diplomatic relations with Doha, among other measures. The Gulf countries said that Qatar was supporting terrorism. The dispute relates to Qatar’s support for the Muslim Brotherhood, which is an opponent of the Egyptian and Saudi governments in particular. It also tied into Qatar’s relatively closer relations with Iran and Turkey.