He denied Western accusations that Russia invaded Crimea prior to the referendum, saying Russian troops were sent there in line with a treaty with Ukraine that allows Russia to have up to 25,000 troops at its Black Sea Fleet base in Crimea.
Speaking at the Kremlin, Putin repeatedly emphasized that the Crimea referendum was in full accordance with international law and that the West has crossed the line on Ukraine.
"We need to be as strong as ever in future, to rise up to challenges. We will be facing some opposition from the West" Putin said.
Earlier, he took the first official steps to make Crimea part of the Russian Federation, approving a draft bill that would formalize the annexation of the Black Sea peninsula.
A notice of the draft bill was posted Tuesday morning on a Russian government website.
The United States and the European Union have so far announced asset freezes and other sanctions against Russian and Ukrainian officials involved in the crisis in Crimea, which was part of Russia from the 18th century until Soviet leader Nikita Khrushchev transferred it to Ukraine in 1954.
On Sunday, some 97% of voters in Crimea backed a referendum for a union between the largely ethnic-Russian peninsula and the huge neighboring country, according to election officials there, but the U.S. and Europe maintain that the election was illegal and have refused to recognize it.
Some experts have speculated that Putin's ultimate ambition is to protect ethnic Russians across the former Soviet empire.
"Putin is prepared to keep on pushing," Fiona Hill, a Russia expert at the Brookings Institution in Washington, told the Associated Press.
"I wouldn't be at all surprised if he moves into other points into eastern Ukraine."
Vice President Joe Biden traveled to Poland Tuesday on a trip designed to show U.S. resolve against Russia's intervention in neighboring Ukraine.
He is meeting with Polish Prime Minister Donald Tusk and President Bronislaw Komorowski.
He'll also meet with Estonian President Toomas Hendrik Ilves.
Later, Biden will fly to the Baltic nation of Lithuania to meet with President Dalia Grybauskaite and Latvia's president, Andris Berzins.
Latvia and Estonia share borders with Russia, and Poland and Lithuania are nearby.
Source: USA Today