Alexander Konakov, the head coach of the Russian national sambo team, told Russia's official state news agency TASS that Mukhtar Gamzaev, Ezher Enchinov and Dmitry Samoilov have all been unable to come into the host country.

They were due to compete in the men's 57 kilograms, 62kg and 82kg categories respectively.

"This situation puzzles all of us and we will be making further inquiries as we still have no explanations regarding this decision," Konakov said.

"This situation is something new for us because our athletes are always taking part in tournaments abroad.

"When we learn the reasons we will involve the international and the European sambo federations.

"It would have been understandable if only one wrestler was denied an entry visa because of failing to properly fill out application documents, but when the issue is about several athletes, we see a negative tendency."

International Sambo Federation (FIAS) President Vasily Shestakov told TASS that the world governing body would launch its own investigation into the matter.

He also said FIAS would provide all the necessary support to the three athletes affected.

"The International Sambo Federation will render assistance to Russian athletes, who had been denied entry visas to Greece," Shestakov said.

"Sport is the activity that has served as a connection between countries even through the most difficult times.

"Even when we think about the times of the Cold War, our athletes were never denied visas to travel abroad.

"It is unclear at the moment on what grounds this decision was based and whether it was connected with sanctions against Russia, therefore we need to thoroughly study this matter."

Five members of the Russian delegation for the event have also reportedly been denied entry visas by the Greek consulate.

Sergey Eliseev, President of the European Sambo Federation and the Russian Sambo Federation, said the decision will be protested.

"We cannot understand why this happened because the whole team had filed documents with the embassy as usual," he told TASS.

"There were no questions for us but at the last moment several people were unable to just obtain visas.

"They had booked a flight and they had been sitting at the consulate until the last day, when [diplomats] came out and said that 'we are not issuing visas to you' since 'a European championship is not such a milestone event which requires visas to be obtained for it'.

"We just cannot understand this as the event starts tomorrow, so we will write a note of protest or something like this.

"We will try to find out and will inform Sports Minister Pavel Kolobkov and Foreign Minister [Sergey] Lavrov.

"We want to protect our athletes."

The incident comes just a couple of months after Mikhail Degtyarev, chairman of the State Duma’s Committee for Physical Culture, Sports, Tourism and Youth Affairs, called the denial of United States visas for Russian wrestlers hoping to compete at the United World Wrestling Men’s Freestyle Wrestling World Cup in Iowa a "blow to global sports".

It came after Russian Foreign Ministry spokesperson Maria Zakharova had claimed the US Embassy in Moscow refused to interview Russian wrestlers who had qualified for the competition - a prerequisite for obtaining entry visas to America.

The situation surrounding the Russian wrestlers followed an increase in tensions between the US and Russia after the Russian Government's alleged involvement in the poisoning of former double agent Sergei Skripal in the British city of Salisbury in March. 

The 2018 European Sambo Championships brings together the continent's leading athletes to battle it out for honours across 27 different categories.

The three-day event is scheduled to take place at the Ano Liossia Olympic Hall.

The opening day of action will see medals awarded in nine categories, comprising the men’s 52kg, 68kg and 90kg, the women’s 48kg, 60kg and 72kg, and combat sambo’s 57kg, 74kg and 100kg.

Taking centre stage on Saturday (May 19) will be the men’s 57kg, 74kg and 100kg, the women’s 52kg, 64kg and 80kg and combat sambo’s 62kg, 82kg and over 100kg.

Rounding out proceedings on Sunday (May 20) will be the men’s 62kg, 82kg and over 100kg, the women’s 56kg, 68kg and over 80kg and combat sambo’s 52kg, 68kg and 90kg.

Last year’s European Sambo Championships were held in Belarus’ capital Minsk, where Russia claimed 18 of the 27 gold medals on offer.

Russia is very much the dominant force in sambo, which originated in the Soviet Union in the 1920s when soldiers of the then-Soviet Army developed their own hand-to-hand combat technique.

Sport sambo is similar to judo, but with some variations in rules, protocol and uniform.

Combat sambo, meanwhile, resembles modern mixed martial arts, including extensive forms of striking and grappling, and is for men only.