Russia's growing military involvement in the Syria conflict is expected to be high on the agenda as Nato defence ministers meet in Brussels.
It comes after Nato member Turkey complained that Russian jets had repeatedly violated its airspace.
Ministers are also expected to review a range of measures introduced in the wake of the Ukraine crisis.
BBC defence correspondent Jonathan Marcus says the alliance aims to make clear it will respond to any challenge.
Nato ministers are expected to express their solidarity with Turkey and also address increased concern among Baltic members following Russia's involvement in eastern Ukraine.
UK Defence Secretary Michael Fallon is expected to announce that Britain is ready to make a long-term troop deployment to the Baltic republics, our correspondent says.
But, he adds, ministers are meeting amid a deepening sense of crisis.
High-stakes gamble - Jonathan Marcus says the two incursions highlight the risk of a potential clash
What can Russia's air force achieve? Why should Russia be able to do any better than the US-led coalition?