President Obama warned Russia Thursday that there would be consequences for aggression against Ukraine but he carefully avoided any threat of a military response.

"There will be costs for any military intervention in Ukraine," Obama said from the White House, but he did not specify what those costs might be.

There have been no alerts thus far to U.S. and NATO troops in Europe in response to massive Russian troop movements on Ukraine's border and to reports that Russian sympathizers, possibly backed by Russian troops, had moved to occupy two airports in the Crimea.

"We are now deeply concerned by reports of military movements taken by the Russian Federation inside Ukraine," Obama said in reference to the Crimea.

Any such movements "would be a clear violation of Russia's commitment to respect the independence and sovereignty and borders of Ukraine and of international laws," Obama said in a late afternoon statement from the White House.

Obama added that "I also commend the Ukrainian government's restraint" in avoiding a confrontation with Russian troops or their supporters in Russian-speaking eastern Ukraine.

In earlier phone calls to Russian Foreign Minister Sergei Lavrov, Secretary of State John Kerry said Moscow would be making a "grave mistake" in any effort to restore ousted Ukrainian President Victor Yanukovych, who fled to Russia.

In Russia, Yanukovych claimed he was the victim of a "bandit coup," the Associated Press reported.

In Kiev, Oleksandr Turchynov, Ukraine's acting head of state, said "I am personally addressing President (Vladimir) Putin to stop the provocation and call back the military from the autonomous Republic of Crimea, and work exclusively within the framework of the signed agreements" on non-intervention.

Also in Kiev, Ukraine's newly-named Interior Minister Arsen Avakov accused Russia of military aggression. In a Facebook posting, Avasov said of the actions in Crimea that "I can only describe this as a military invasion and occupation."

Earlier, House Republican Leader Eric Cantor, R-Va., called reports of Russia military movements of "grave concern" and he also spoke of consequences.

Among those consequences could be economic sanctions for "Russian individuals and entities who use force or interfere in Ukraine's domestic affairs," Cantor said.