Four British Royal Air Force Typhoon fighters landed in Lithuania, while four French Rafale jets touched down in the northern Polish city of Malbork.
British defence minister Philip Hammond said the move would "provide reassurance to our NATO allies in eastern Europe and the Baltic states".
"In the wake of recent events in Ukraine, it is right that NATO takes steps to reaffirm very publicly its commitment to the collective security of its members."
Lieutenant Colonel Simon Hulme of the Royal Air Force, the mission chief in Lithuania, said it will be "business as usual" for the 168 British personnel deployed at the northern Siauliai air base.
More From This Section
Just five kilometres (three miles) away in the city centre, pensioner Brone Simanauskiene said NATO had allayed some of her concerns about Russia's intentions.
"We are concerned, but I believe the increased NATO presence will make us safer. I am glad that more jets will arrive," she told AFP before the British jets landed.
Student Ernestas Tuzinas, 22, said NATO must do more to deter Russia from invading Moldova or even the Baltic states, which spent five decades under Soviet occupation until 1991 and joined NATO and the European Union in 2004.
Before the Ukraine crisis erupted, four jets belonging to NATO allies took turns guarding the airspace above the Baltic states, which have grappled with a shortage of fighter planes.