VIENNA (AP) — The European Union’s main representative at the nuclear talks with Iran says he was briefly detained with colleagues at Frankfurt Airport, in breach of diplomatic rules.

Enrique Mora of Spain, who has long led the EU delegation at the talks in Vienna, said the incident happened Friday morning as he was trying to make a connecting flight from Tehran to Brussels.

Mora wrote on Twitter that he received “not a single explanation” from German authorities for why he was detained. “An EU official on an official mission holding a Spanish diplomatic passport. Took out my passport and my phones.”

Mora said the EU Ambassador to the U.N. in Vienna and the head of the EU’s Iran task force were also detained.

“We were kept separated,” he wrote. “Refusal to give any explanation for what seems a violation of the Vienna Convention.”

Neither German police nor Germany’s Foreign Ministry responded immediately to requests for comment.