Russia's lower house of parliament, the State Duma, has overwhelmingly ratified a treaty to annex Crimea from Ukraine.
The lawmakers voted on the measure Thursday, and the parliament's upper house, the Federation Council, will hold a similar vote on Friday.
Crimeans voted in a regional referendum last Sunday to declare independence from Ukraine in hopes of joining the Russian Federation.
On Tuesday, President Vladimir Putin and Crimean leaders signed the treaty making Crimea part of Russia after Mr. Putin declared in a speech that the peninsula had always been an "inalienable" part of Russia. The Kremlin said later Tuesday that the treaty was in force from the day it was signed.
United Nations Secretary-General Ban Ki-moon, who is visiting Moscow, expressed deep concern - saying the referendum will only exacerbate "an already complex and tense situation."
Meanwhile, the European Union is readying further sanctions against Russia over its annexation of the Crimean peninsula.
German Chancellor Angela Merkel told her nation's parliament Thursday the EU is prepared to move to "Level 3" measures, which would include economic sanctions, if the situation worsens.
The EU and the United States have already imposed travel bans and asset freezes on Russian officials deemed responsible for the incursion into Crimea.
Chancellor Merkel said the Group of Eight forum of leading economies is effectively suspended as long as the diplomatic standoff with Russia continues. Russia is part of the G8, along with Britain, Canada, France, Germany, Italy, Japan and the United States.
Mr. Ban is meeting Russian President Vladimir Putin and Russian Foreign Minister Sergei Lavrov in Moscow, before traveling to Ukraine Friday.
Meanwhile, President Turchynov says the commander of Ukraine's navy has been freed after being held by Russian forces and Crimean authorities at the navy's headquarters in Crimea. He said Rear Admiral Sergei Haiduk was released, along with an unspecified number of civilians.
The group was detained after the Ukrainian naval base in the Crimean port of Sevastopol was seized Wednesday. Reports indicated pro-Russian militiamen -- Crimea's so-called "self-defense" forces -- were behind the takeover, but President Turchynov's statement suggests Russian forces were also involved.
After the seizure, which faced no resistance from Ukrainian servicemen, Ukraine's security chief said the country has drawn up plans to evacuate its outnumbered military personnel from the Crimean peninsula.
In announcing the withdrawal, Andriy Parubiy -- secretary of Ukraine's National Security and Defense Council -- said Kyiv will seek United Nations support in turning the peninsula into a demilitarized zone. He also said Ukraine is planning to hold military maneuvers "with our allies," but did not elaborate.
U.S. Vice President Joe Biden told reporters in Lithuania Wednesday that Russia will face "increasing political and economic isolation" as long as it continues on what he called "its dark path."