Obama traveled to Europe this week to meet with his European counterparts to discuss the growing tension with Russia and how to proceed in their response to what they call an illegal annexation.
"Europe and America are united in our support of the Ukrainian government and the Ukrainian people. We're united in imposing a cost on Russia for its actions so far," said Obama in a press conference Monday.
The United States has already imposed numerous sanctions on Russian officials and business, as well as visa bans for those in Russian President Vladimir Putin's inner circle. The EU has also imposed sanctions and warned they could be extended.
Cameron also said that he is focused on the next step in the response to Russia and that the country needs to change its course.
"Well, we should be clear, there's not going to be a G-8 summit this summer in Russia. That's absolutely clear. We'll be meeting tonight, the 7 other countries of the G-8, to determine the way forward but, frankly, it is Russia that needs to change course." said Cameron.
The White House announced Monday afternoon that the G-7 members -- U.S., Britain, France, Germany, Italy, Canada and Japan -- have decided to suspend Russia's membership in the group.