Russia has dismissed Canada's complaint that three Russian military aircraft acted "provocatively" by flying near a Canadian navy frigate in the Black Sea.
HMCS Toronto was taking part in NATO exercises off the southern coast of Ukraine at the weekend when two Russian Su-24 fighter jets and an AN-26 surveillance aircraft flew by.
Canada's Defence Minister Rob Nicholson said the aircraft circled the frigate. He said the jets posed no threat, but the move was "unnecessarily provocative and risk escalating tensions even further".
Mr Nicholson said Canada and its allies were taking part in reassurance measures as a result of Vladimir Putin's "military aggression and invasion of Ukraine".
Russian ministry spokesman Igor Konashenkov told news agencies on Tuesday that its jets were indeed flying in the area - but were behaving "strictly in line with international rules".
"The planes' flight path passed through the area where the Canadian naval ship Toronto was, but without making an approach on the foreign military vessel," he said.
Relations between Moscow and Ottawa have been strained by Canada's decision to impose sanctions on Russia over its role in the Ukrainian crisis.
An uneasy ceasefire in eastern Ukraine between government forces and pro-Russian separatists appears to be holding despite sporadic violations in rebel-held Donetsk.
Four Ukrainian servicemen have been killed and 29 injured since the truce was announced on Friday, according to Ukraine's military-medical official Vitaly Andronaty.
Both sides say they are observing the ceasefire and blame each other for any violations. The truce includes an agreement on the release of prisoners on both sides, the delivery of humanitarian aid and the withdrawal of heavy weapons.
Ukrainian President Petro Poroshenko has said the conflict cannot be solved by military means alone.
"We should understand that it is impossible to win the conflict only by military means," he said.
"The more we increase the pressure, the more Russian troops come into our territory. If you ask me the quickest way to make stability and peace here it's very simple: withdraw foreign troops and close the border."
The ceasefire has raised hopes of an end to the five-month conflict which, according to the UN, has killed more than 3,000 people.
