With Russian armed forces holding a tight grip on the peninsula, the pro-Russian regional Parliament in Crimea voted behind closed doors on Thursday to secede from Ukraine and become part of Russia and scheduled a public referendum on the issue for March 16.

President Obama on Thursday declared that a referendum asking Crimean voters if they want to join Russia would violate Ukraine's constitution and international law, and he promised to keep ramping up the pressure on Russia until it stands down in the region, Los Angeles Times reports.

“In 2014, we are well beyond the days when borders can be redrawn over the heads of democratic leaders,” the President said in the White House briefing room.

Obama also said he is tightening sanctions as part of an effort to “impose a cost” on Russia for its intervention, and he praised the European Union for taking similar steps to penalize those involved in the dispute.

Ukrainian President Oleksandr Turchynov scoffed at the plan for a referendum, noting that Russian forces had taken control of Crimea’s borders and ports and were blocking Ukrainian military bases and occupying other security installations.

“This will be a farce,” - he said in a televised address. This will be false. This will be a crime against the state.”