Speaking during a visit to Manila, Russian Foreign Minister Sergei Lavrov said Russia was "truly amazed" at the criticism, saying explorers worldwide have always planted flags.
Lavrov was responding to comments by Canadian Foreign Minister Peter MacKay, who dismissed the expedition as a "show" and said planting flags to claim territories was a practice more suited to the 15th century.
U.S. State Department spokesman Tom Casey said Russia was entitled to submit its territorial claim to the United Nations, but he said the flag-planting had no legal standing.
Two Russian mini-submarines descended more than four kilometers beneath the ice to plant a titanium flag at the bottom of the Arctic Ocean.
Moscow has said the expedition would help prove that the North Pole is a geological extension of Russia. If proven, that would help advance Russia's claims to oil, gas, and mineral resources on the Arctic seabed.
Oceanographer Lindsay Parson told RFE/RL that the expedition has little bearing on Russia's legal claims to the territory.
(compiled from agency reports)