Oleg Salagay, Russia's Deputy Health Minister, has been denied entry to Denmark at Copenhagen airport on his way to a World Health Organisation (WHO) conference.

"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 said, as Politico reports. Condemning the incident, the embassy demanded an apology from the Danish authorities.

The Danish Foreign Ministry has launched an investigation, local media report.

The WHO conference is a regional meeting on "applying behavioural and cultural insights for health" held in Copenhagen September 12-14.

The refusal emerged amid a dispute between Denmark and Russia over the number of officials working in each other's embassies.

On 1 September, the Danish Foreign Ministry informed Russian Ambassador Vladimir Barbin that the diplomatic mission in Copenhagen should be reduced to the level corresponding to the staff of the Danish embassy in Moscow, i.e. to 5 diplomats and 20 administrative and technical staff.

The Danish Foreign Ministry explained that negotiations on expanding the embassy staff in Denmark had failed because Moscow was constantly trying to send its intelligence officers to the country.

Moscow merely claimed that it would "draw conclusions" from the decision.

The Russian Embassy in Copenhagen has until September 29 to reduce its staff.