Crimea and Sevastopol are now officially part of the Russian Federation, the Kremlin said in a statement, citing today's signing ceremony involving Russian President Vladimir Putin, the Prime Minister of Crimea and the mayor of Sevastopol.

Crimea is an autonomous region within Ukraine with a majority Russian-speaking population. It has its own parliament, but the Ukrainian government had veto power over its actions.

But with political instability and demonstrations rocking Ukraine in the past several months, President Viktor Yanukovych was pushed out of office and observers charged that Russia saw its chance to annex the strategic territory. A hastily called referendum Sunday resulted in 96.7% of the region's voters saying they wanted to become part of Russia, according to the Crimean Electoral Commission.

The United States and other Western powers have said Sunday's vote was illegal and placed sanctions on more than two dozen Russian officials and their allies in Crimea.