Russia’s Deputy Health Minister Oleg Salagay was turned away at Copenhagen airport en path to a World Health Organization convention in Denmark.

“O. Salagay, State Secretary and Deputy Minister of Health, was supposed to attend this event. However, he was refused entry to Denmark at Kastrup airport,” the Russian embassy in Denmark wrote on Telegram. Condemning the incident, the embassy demanded an apology from Danish authorities.

The Danish overseas ministry is investigating the matter, in keeping with local media.

The WHO conference is a regional assembly on “applying behavioral and cultural insights for health” and takes place in Copenhagen from September 12 to 14.

The refusal comes on the again of a battle between Denmark and Russia over the variety of officers working at one another’s embassies.

During the visa negotiations for workers of Denmark’s embassy in Moscow, Russia repeatedly filed visa requests to Copenhagen to fill the Russian embassy there with “undeclared agents” or spies, Danish Foreign Minister Lars Løkke Rasmussen told the news website DR earlier this month.

The Russian embassy in Copenhagen now has till September 29 to scale back its employees to 5 diplomats and 20 administrative and technical employees, to deliver it according to the Danish embassy in Moscow, Rasmussen added.