In Brussels, NATO's secretary-general, Anders Fogh Rasmussen, said Russia's actions have violated a U.N. charter. He said the alliance was re-evaluating its relationship with Russia.
Beyond economic sanctions and visa bans, freezing Russian assets, and trade and investment penalties, Kerry said Moscow risks being booted out of the powerful Group of Eight group of world powers as payback for the military incursion.
Former Ambassador Nicholas Burns said, "Putin's not going to back off. ... What can President Obama do? Be very minded in opposition. We can't follow a military policy. This has to be diplomatic."
Several U.S. senators also called for bolstered missile defense systems based in Poland and the Czech Republic.
Russia is "going to be inviting major difficulties for the long term," said Kerry. "The people of Ukraine will not sit still for this. They know how to fight."
Sen. Marco Rubio, R-Fla., discussing the potential of U.S. military strikes against Russian troops in Crimea, said, "I don't think anyone is advocating for that." One of the administration officials indicated that the U.S. was not weighing military action to counter Russia's advances, saying the Obama administration's efforts were focused on political, economic and diplomatic options.
Rubio and fellow GOP Sen. Lindsey Graham of South Carolina said the Obama administration should return to plans it abandoned in 2009 to place long-range missile interceptors and radar in Poland and the Czech Republic.
Russia suggested the program was aimed at countering its own missiles and undermining its nuclear deterrent. The White House denied that and has worked instead to place medium-range interceptors in Poland and Romania — aimed at stopping missiles from Iran and North Korea.