Spain is coming under criticism for reportedly preparing to allow the refuelling of Russian warships en route to bolstering the bombing campaign against the besieged Syrian city Aleppo.
Warships led by the smoke-belching aircraft carrier Admiral Kuznetsov are expected to take on fuel and supplies at the Spanish port of Ceuta after passing through the Straits of Gibraltar on Wednesday morning, according to the Daily Telegraph.
The report comes after Royal Navy vessels monitored Russian warships as they began to move through the English Channel last week.
The Russian vessels were shadowed by the Navy as they passed through the Dover Strait - one of the busiest seaways in the world.
Sir Gerald Howarth, a former defence minister, told the Telegraph it would be "wholly inappropriate" for a Nato member to refuel the vessels.
Former Royal Navy chief Lord West told the newspaper: "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 told the newspaper: "Russian navy vessels have been making calls in Spanish ports for years."
The Telegraph added that the Spanish government said it was reviewing the Russian request.
A UK Government spokesman said: "Access to Spanish ports is a matter for the Spanish authorities. HMG has previously expressed concerns to the Spanish government about its hospitality to the Russian navy when we have concerns about Russia's military activity.
"We are clear that the UK's relationship with Russia should not be business as usual."
Last week's Russian passage through the Channel came after Theresa May condemned Vladimir Putin's aggression in Syria, accusing Moscow of being behind "sickening atrocities" in support of Bashar Assad's regime.
Nato said the prospect of Russia's only aircraft carrier heading to the region does not "inspire confidence" that Moscow is seeking a political solution to the Syrian crisis.
Russian defence minister Sergei Shoigu said in September that the Admiral Kuznetsov-led Northern Fleet would be joining a taskforce in the Mediterranean.
According to the Russian news agency Tass, he told a defence board meeting that the plan was to bolster the Mediterranean fleet's "combat capabilities".
A statement from the fleet to the agency on October 15 said the group also consisted of the Pyotr Velikiy battlecruiser, the Severomorsk anti-submarine ship, the Vice-Admiral Kulakov destroyer and other support vessels.