Belbek, Crimea: More than a dozen SU-27 and SU-30 fighter jets which Russia is deploying to boost its air force, amid heightened tensions with Ukraine, have arrived in Crimea.

Tensions between Moscow and Kiev have risen in the past weeks after Russia seized three Ukrainian navy ships and their crews on November 25 in an incident which Moscow and Kiev have blamed on each other.

Russian Foreign Minister Sergei Lavrov has alleged Ukraine was preparing "a provocation" near Crimea before the end of the year.

Early in December, Ukraine President Petro Poroshenko said Russia had deployed "more than 80,000 troops, 1400 artillery and multiple rocket launch systems, 900 tanks, 2300 armoured combat vehicles, 500 aircraft and 300 helicopters" along their common border.