Lew said the administration was ready to supplement emergency IMF loans to cushion the impact economic reforms would have on vulnerable Ukrainians.
"The United States is prepared to work with its bilateral and multilateral partners to provide as much support as Ukraine needs to restore financial stability and return to economic growth if the new government implements the necessary reforms," Lew said during a speech Sunday night to the annual policy conference of AIPAC, America's largest pro-Israel lobbying group.
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."
Still, it was clear that few in the West were prepared to respond immediately to Putin with military force.
At the Vatican, Pope Francis used his traditional Sunday midday appearance in St. Peter's Square to urge world leaders to promote dialogue as a way of resolving the crisis in Ukraine.
Republican Sen. Marco Rubio, 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.
