Donald Trump has warned there 'could be big trouble' after Russia flew three fighter jets into neighbouring Estonia in a 'reckless' and 'brazen' attempt to intimidate the Baltic state.

The defensive alliance rushed to mobilise duty warplanes today to repel the Russian jets which violated its member's airspace.

Tallinn said that three Russian MiG-31 fighter jets violated the airspace of NATO member Estonia over the Gulf of Finland for 12 minutes on Friday.