Russian President Vladimir Putin has said Russia's border "doesn't end anywhere", addressing a televised awards ceremony for geography students.
"That was a joke," Mr Putin said amid applause and laughter from the audience at the glitzy ceremony.
He was asking a nine-year-old boy: "Where does Russia's border end?" The boy had said "at the Bering Strait". Mr Putin then provided his own answer.
Mr Putin has pledged to defend ethnic Russians wherever they live.
In July 2014, three months after Russian troops annexed Ukraine's Crimea peninsula, he spelled out his doctrine to Russian ambassadors.
"I would like to make it clear to all: our country will continue to actively defend the rights of Russians, our compatriots abroad, using the entire range of available means - from political and economic to operations under international humanitarian law and the right of self-defence."
Nato and Western leaders accuse the Kremlin of sending regular troops and heavy weapons to pro-Russian rebels in eastern Ukraine. The Kremlin has repeatedly denied that, insisting that any Russian troops there are "volunteers".
Just before his comment about Russia's border, President Putin asked five-year-old Timofey Tsoi to name the country whose capital is Ouagadougou.
Timofey correctly answered "Burkina Faso", but struggled when asked what the country's old name was. Mr Putin helped him out, saying: "Upper Volta! Good lad!"
In its dying days, the Soviet Union was sardonically described as "Upper Volta with rockets".
Both boys had distinguished themselves in televised geography quizzes. The ceremony was staged by the Russian Geographical Society.