SOFIA (Reuters) – Iran has denied access to its airspace to a Bulgarian government jet taking a delegation led by Prime Minister Boyko Borissov to Tehran’s regional arch-enemy Saudi Arabia, Sofia’s foreign minister said on Wednesday.

Ekaterina Zaharieva told reporters the plane had all necessary permits to fly over Iran en route to Riyadh late on Tuesday but once it entered Iranian airspace it was asked by Iranian authorities to leave.

Zaharieva, part of the delegation on board, said the aircraft had to return to Turkey after what she called an “inexplicable last-moment refusal” by Iran. She said the plane had to get permission to fly through Iraqi airspace, to the west of Iran, before it could reach its final destination.

She said Tehran had told Sofia the air access refusal was due to a slight deviation of the plane from its planned route, but Bulgarian authorities disagreed and had summoned the Iranian charge d‘affaires to Bulgaria for an explanation.

“The government aircraft had secured all the necessary diplomatic permissions to fly over Iranian airspace.”

Borissov is the first Bulgarian prime minister to visit Saudi Arabia. Bulgaria will take the European Union’s rotating presidency from January for six months.

The Sunni Muslim kingdom of Saudi Arabia and Shi‘ite Muslim Iran support rival sides in wars and political crises throughout the Middle East.