Former US secretary of state Hillary Clinton on Tuesday taunted her old nemesis, Russian President Vladimir Putin, over the expansion of NATO since his invasion of Ukraine.

"Too bad, Vladimir. You brought it on yourself," Clinton said in an aside as she returned to the State Department for the unveiling of her official portrait.

"It was such a point of contention. And we always said, people are not forced to join NATO, people choose and want to join NATO," she said.

Finland and Sweden sought to join NATO after Russia's February 2022 invasion of Ukraine, which had unsuccessfully sought to join the Western alliance whose members pledged to defend one another if attacked.

Putin has cited Ukraine's flirtation with NATO as a reason for the invasion, which has been met with strong Western support for Kyiv including billions of dollars in weapons.

Clinton took office in 2009 as the top diplomat in Barack Obama's administration and quickly sought to "reset" relations with Russia, which had been damaged by Moscow's attack the previous year of another former Soviet republic, Georgia.

But relations sharply deteriorated by the end of her tenure as an increasingly authoritarian Putin in 2012 accused her personally of fomenting protests by opposition leaders who rejected the results of parliamentary elections in which his party cruised to victory.

Clinton was the Democratic presidential nominee who lost to Donald Trump in 2016. A US Senate panel concluded afterward that Moscow sought to interfere in the election to help Trump win.