MOSCOW — Russia signaled for the first time on Friday that it was prepared to annex the Crimea region of Ukraine, significantly intensifying its confrontation with the West over the political crisis in Ukraine and threatening to undermine a system of respect for national boundaries that has helped keep the peace in Europe and elsewhere for decades.

Leaders of both houses of Russia’s Parliament said that they would support a vote by Crimeans to break away from Ukraine and become a region of the Russian Federation, ignoring sanction threats and warnings, from the United States and other countries, that a vote for secession would violate Ukraine’s Constitution and international law. The Russian message was yet another in a series of political and military actions undertaken over the past week that outraged the West, even while the Kremlin’s final intentions remained unclear.

As new tensions flared between Russian and Ukrainian forces in Crimea, the moves by Russia raised the specter of a protracted conflict over the status of the region, which Russian forces occupied last weekend, calling into question not only Russia’s relations with the West but also post-Cold War agreements on the sovereignty of the nations that emerged from the collapse of the Soviet Union.

The developments underscored how quickly the crisis has evolved. Earlier this week, President Vladimir V. Putin of Russia had said he did not foresee the possibility of the Crimean Peninsula becoming part of Russia. But on Friday, Russia’s parliamentary leaders, both strong allies of Mr. Putin, welcomed a delegation from Crimea’s regional assembly and declared that they would support a vote to break away from Ukraine, now scheduled for March 16.