NATO Secretary-General expressed concern over the arrangement
A Russian naval tanker has sailed past a Spanish port after pressure was put on Madrid to deny entry to the ship.
The Osipov is part of the Admiral Kuznetsov carrier group, which is en-route to the eastern Mediterranean to carry out bombing missions over Syria.
It was believed she could sail into the port of Ceuta, a Spanish enclave on the north African coast, to re-supply.
This threatened a diplomatic incident after the NATO Secretary-General asked the Spanish government to reconsider its position.
Jens Stoltenberg said: "It is for each nation to decide whether these ships can get supplies and re-fuelling in different harbours along the route towards the eastern Mediterranean.
"But, at the same time, we are concerned and I have expressed this very clearly, about the potential use of this battle group to increase Russia's ability and to be a platform for airstrikes against Syria."
Maritime tracking maps show the Osipov east of Ceuta and sailing further into the Mediterranean on Wednesday.
A Russian tanker, also part of the Carrier group, is still in the Atlantic, close to the Strait of Gibraltar. She is expected to pass through in the next 24 hours and could potentially dock in Ceuta.
It comes after British navy vessels shadowed Russian warships as they passed through the English Channel last week.
Gerald Howarth, a British former defence minister, told the UK's Daily Telegraph it would be "wholly inappropriate" for a NATO member to refuel the vessels.
Former Royal Navy chief Alan West said: "There are sanctions against Russia and it's an extraordinary thing for a NATO ally to do."
Spain's foreign ministry told the Telegraph requests from the Russian navy were considered on a "case by case basis".
A spokesman said: "Russian navy vessels have been making calls in Spanish ports for years."
Russian defence minister Sergei Shoigu said last month that its Northern Fleet would be joining a task force in the Mediterranean.
According to the Russian news agency Tass, he told a defence board meeting the plan was to bolster the Mediterranean fleet's "combat capabilities".
A statement from the fleet to the agency on October 15th said as well as the Admiral Kuznetzov, the group included a battlecruiser, a destroyer, an anti-submarine ship and support vessels.