Ukraine now says flights will end at midnight on Saturday, after last-minute crisis talks failed.
Up to 70,000 passengers a month will be affected.
The sanctions are intended to punish Russia for annexing Crimea and supporting armed rebels in eastern Ukraine. The fact that they have been introduced now, when a ceasefire is finally holding on the ground, shows how bitter relations remain.
Russia has accused Ukraine of shooting itself in the foot with the move, pointing out that most passengers are Ukrainian travelling to work in Russia, visiting relatives or in transit.
But two-thirds of all passengers travel on Russian airlines.
Russia`s transport minister has estimated that the loss in ticket sales to both countries will run to around $110m (£73m) a year.
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