Canadian fighter jets will be patrolling the edge of Russian airspace next week as part of NATO's response to the unravelling situation in Ukraine.
At least four of the six CF-18s sent overseas by the Harper government earlier this year have arrived at Siauliai Air Base in Lithuania, where they will fly air policing missions over the Baltic states.
The formal handover of responsibility is expected to take place early next week.
The Canadian jets will be working alongside fighters from Portugal, Germany and Belgium, which will be carrying out flights from bases in another Baltic state.
The missions are meant to reassure European allies unnerved by Russia's seizure of the Crimean Peninsula, as well as the military action currently unfolding in eastern Ukraine.
The jets, which had been based in Romania on a training exercise, are tasked with defending Estonian, Latvian and Lithuanian airspace because those countries are unable to do so on their own.
The deployment comes against the unfolding backdrop of heavy fighting and an apparent Russian invasion, and brings Canadian fighters as close to Russian territory as they've been since the crisis began.
Ukraine claims Russian incursion
Ukrainian President Petro Poroshenko called an urgent session of the national security council on Thursday after two columns of Russian tanks reportedly entered the country's southeast earlier in the day.
"Destabilization of the situation and panic, this is as much of a weapon of the enemy as tanks," Poroshenko told the security council, according to the Interfax news agency.
Russia's latest escalation is an outrage that will have repercussions, Foreign Affairs Minister John Baird said as he called on President Vladimir Putin's regime to halt its apparent invasion, as well as the flow of arms to separatists.
The Harper government will review what further sanctions and other measures can be taken, Baird said, but he stopped short of specifics about what sort of response could be expected.
Last spring, Prime Minister Stephen Harper described the annexation of Crimea as a "slow-motion invasion" of Ukraine. Baird said the events of the last few days indicate the Russians have accelerated their efforts.
"This is absolutely unacceptable, irresponsible and absolutely reckless," he said in a conference call from Zagreb, Croatia.
"It is also deeply and shamelessly dishonest. While Russian President Putin talked about ceasefires with President (Petro) Poroshenko in Minsk, his military was busy fighting on Ukrainian soil."
NATO tracks Russian troops
NATO estimates that as many as 1,000 Russian troops are fighting inside Ukraine with an additional 20,000 clustered on the border as support — or reinforcements.
"Over the past two weeks we have noted a significant escalation in both the level and sophistication of Russia's military interference in Ukraine," said Dutch Brig.-Gen. Nico Tak.
"We have also detected large quantities of advanced weapons, including air defence systems, artillery, tanks, and armoured personnel carriers being transferred to separatist forces in Eastern Ukraine."
The military alliance also released a series of satellite images supporting its claim.
Major U.S. banks, meanwhile, reported they were the target of a massive cyberattack that defence officials suggested may have originated in Russia.
Defence analysts expressed little surprise at that revelation, noting Russia's military strategy involves the use of cyberwarfare to disrupt and cripple adversaries.
Baird called the recent events a "significant provocation" in advance of next week's NATO summit in Wales, where the alliance's leaders are expected to hold a special meeting with Poroshenko.
Asked to characterize the latest developments, Baird described Russia's move as an "incursion" and an "invasion," but stopped of short declaring it an act of war.
Ukraine is not a member of NATO, unlike other eastern European nations; the alliance is not automatically obliged to come to its defence.