"I very much hope that I am not obliged to use this right and that through political and diplomatic means we can solve all the acute problems in Ukraine," he said in his annual televised phone-in with the nation, in a signal the option was on the table.
The upper house of parliament on March 1 authorised the Russian leader to send troops into Ukraine after pro-Kremlin president Viktor Yanukovych was ousted, and Moscow later went on to annex Ukraine's Russian-speaking Crimean peninsula.
Russia has now massed tens of thousands of troops at the border and has warned Kiev's untested new leaders -- whom it does not recognise as legitimate -- not to unleash force in Ukraine.
Accordingly, Kerry warned Russia that if there was no progress on deescalating the crisis in Ukraine, "there will be additional sanctions, additional costs."
The United States and European Union have already imposed punitive sanctions on key Russian and Ukrainian political and business officials, including members of Putin's inner circle.
And the European Parliament today said the European Union should act "against Russian firms and their subsidiaries, especially in the energy sector, and Russia's EU assets".
So far, though, any further sanctions appear to have been put on hold.
Russia's annexation of the Crimea peninsula last month escalated a crisis that has shaped up to be the worst East-West standoff since the Cold War.
