"We should be clear there's not going to be a G8 summit in Russia," Cameron told reporters.
In a statement, the leaders of the seven nations - Canada, France, Germany, Italy, Japan, Britain and the United States, reaffirmed their support for Ukraine's sovereignty and condemned Russia, reiterating that the annexation of Crimea violates international law.
"We condemn the illegal referendum held in Crimea in violation of Ukraine's constitution," the declaration, issued after a meeting in The Hague, said. "We also strongly condemn Russia's illegal attempt to annex Crimea in contravention of international law and specific international obligations. We do not recognize either."
As its leaders have said, the group said Russia's actions will have "significant consequences" and that they challenge the rule of law worldwide. The countries have already imposed sanctions on Russia but are willing to go further.
"We remain ready to intensify actions including coordinated sectoral sanctions that will have an increasingly significant impact on the Russian economy, if Russia continues to escalate this situation," the group said.
The impact of canceling the summit is unclear. In a CNN poll released last week, 58 percent of Americans opposed canceling the G8.