President Barack Obama directly sanctioned 11 Russian and Ukrainian officials Monday, the latest escalation in the ongoing crisis in Crimea — and the president’s latest attempt to make good on his repeated threats of additional costs on Russians for the situation.

Speaking from the White House, he warned that he’s prepared to go even further if Russian President Vladimir Putin doesn’t reverse course on Crimea.

“Further provocations will do nothing except to further isolate Russia and diminish its place in the world,” Obama said at the White House. “We can calibrate our response on whether Russia chooses to escalate or de-escalate the situation.”

Obama repeated the American position: Russian troops must return to their bases in Crimea, and Putin must accept international monitors and start a dialogue with the new government in Kiev. Neither the United States nor the rest of the international community, he repeated, will accept a Crimean referendum Sunday that showed a suspiciously high figure, greater than 95 percent, voting in support of joining Russia.