Defence Secretary Michael Fallon said that Nato was taking the threat posed by Russia seriously.
"What's happened in the Ukraine is very much a wake-up call which the Nato leaders will be discussing at their summit in a month's time here in the UK," he said.
Mr Fallon said that Britain was contributing Typhoon fighter jets to the Baltic policing mission along with other Nato members.
An RAF surveillance aircraft was also in the sky over Ukraine's eastern border with Russia, he added.
More top news
An 11-year-old boy shot dead his eight-year-old neighbour in a row over a puppy, it is alleged.
Boris Johnson is expected to attack George Osborne's plan to cut tax credits when he addresses the Conservative Party conference on Tuesday.
Incursions by Russian jets into Turkish airspace have prompted a stern response from Nato's most powerful ally.