Britain is expressing concern that its NATO ally Spain is considering refueling a fleet of Russian warships that could be used to ramp up air attacks in Syria.

U.K. Defense Secretary Michael Fallon said Wednesday that "we would be extremely concerned if a NATO member should consider assisting a Russian carrier group that might end up bombing Syria."

Fallon told reporters as Alliance defense ministers gathered in Brussels that "on the contrary, NATO should be standing together."

The Russian aircraft carrier Admiral Kuznetsov and a task group of support vessels have steamed through the North Sea and English Channel in recent days heading to the Mediterranean Sea.

Spain said Wednesday that it is reconsidering whether to allow the flotilla to refuel in its North African enclave of Ceuta.