Russia's upper house of parliament has voted unanimously to approve President Vladimir Putin's request for authorization to use Russian armed forces in Ukraine.
The Kremlin said Putin sought authorization to deploy troops in order to protect the lives of ethnic Russians in Ukraine and Russian armed forces based in Ukraine's Crimea region, until the "normalization" of the political situation there.
Federation Council speaker Valentina Matviyenko said the chamber would also call on Putin to recall the Russian ambassador to the United States.
In the past week, Washington has repeatedly warned Russia against interfering in the Ukrainian crisis. President Barack Obama warned on February 28
that "there will be costs" for Moscow for any Russian military intervention in Ukraine.
There has been no response yet from Washington to the Federation Council vote.
Reacting to the Russian developments, Ukrainian pro-European leader Vitali Klitschko has called for parliament to mobilize the Ukrainian armed forces to counter what he called "Russian aggression."
And the United Nations Security Council said it planned to meet in an emergency session at 2 p.m. New York time on March 1 to discuss the situation.
Earlier on March 1, Ukrainian Defense Minister Ihor Tenyukh said Russia had sent 6,000 additional troops into Crimea, along with 30 armored personnel carriers, since February 28. He said the step had been taken without Ukrainian permission and in violation of Ukraine's territorial integrity.
The Russian move comes after Putin's office said Moscow will not ignore a March 1 request for peacekeeping support made by Serhiy Aksyonov, the pro-Russian prime minister of Ukraine's Crimea region.
Aksyonov also declared that all military, police, border guards, and security services in Crimea should answer only to his orders. He said commanders who disagree should resign.
LIVE BLOG: Ukraine Crisis
Aksyonov also declared a referendum of the peninsula's future had been pushed forward by nearly two months to March 30.
Speaking on March 1 at the first cabinet session of his newly established Crimean regional government, Aksyonov said the referendum was being expedited "due to necessity."
Voters will be asked whether they agree with the statement: "The Autonomous Republic of Crimea has state independence and is a part of Ukraine on the basis of agreements and accords."
Aksyonov was appointed on February 27 by the Crimean parliament amid soaring tensions with the new Ukrainian leadership that took power in Kyiv last week.
WATCH: Serhiy Aksyonov speaks to supporters on February 27.
Later on March 1, acting Ukrainian President Oleksandr Turchynov signed a decree declaring Aksyonov's appointment illegal.
Russia Ramps Up The Pressure
Meanwhile, pro-Russian demonstrators have taken over the regional administration building in the eastern city of Kharkiv, forcing their way into the building, firing tear gas, and breaking windows.
WATCH: Pro-Russian demonstrators storm the Kharkiv administration.
A correspondent for RFE/RL's Ukrainian Service in Kharkiv later said he was attacked by pro-Russian activists on March 1 while conducting a live video report from the building. The attackers accused him of doing "wrong coverage."
The correspondent, who does not want to be identified, said he was beaten and forced to kneel and kiss Russian symbols. The attack was stopped by the chairwoman of the Communist Party branch in Kharkiv, Alla Aleksandrovska. The journalist has reported the incident to the police.
Gunshots were earlier heard in the central square near the building, where thousands of pro-Russian demonstrators gathered waving Russian flags and chanting "Russia! Russia!"
In the eastern city of Donetsk, thousands of pro-Kremlin demonstrators have blocked the regional administration building and replaced a nearby Ukrainian national flag with a flag of the Russian Federation.
In Russia, the State Duma lower house of parliament asked Putin to "take measures to stabilize the situation" in Crimea and "use all available means to protect the people of Crimea from tyranny and violence."
Duma Speaker Sergei Naryshkin said the Duma Council adopted an appeal on March 1 urging Putin to take action. It also said legitimate, democratic elections in Ukraine were now impossible.
Naryshkin said Russian lawmakers were concerned about reports of "unknown armed individuals" attempting to take over local government buildings in Simferopol.
In related news, Russia plans to stop natural-gas deliveries to Ukraine at discounted prices. The Energy Ministry said the Kremlin saw no reason to extend discount prices agreed with ousted pro-Russian President Viktor Yanukovych because of unpaid debts for deliveries.
Earlier on March 1, Gazprom spokesman Sergei Kuprianov said Kyiv might lose its discount deal because of Kyiv's outstanding gas debts.
In December, Russia agreed to reduce gas prices for Ukraine by about a third, from about $400 to $268.50 per 1,000 cubic meters. That was the price Ukraine had paid since 2009.
The gas discount deal was made after Yanukovych spurned an EU trade deal in favor of closer ties to Moscow. According to Kuprianov, Ukraine currently owes $1.55 billion for gas deliveries in 2013 and this year.
Kyiv Decries Russian 'Provocations'
Armed men believed to be Russian troops deployed at key airports in Crimea on February 28. On March 1, the airspace around Simferopol International Airport in Crimea was reportedly closed.
There were reports overnight of Russian transport aircraft carrying hundreds on Russian soldiers into those facilities.
At a cabinet meeting in Kyiv on March 1, Ukrainian Defense Minister Ihor Tenyukh accused Russia of sending 6,000 troops and 30 armored personnel carriers into Crimea since February 28 "without warning or Ukraine's permission, in defiance of the principle of noninfringement of state borders."
For his part, Ukrainian Prime Minister Arseniy Yatsenyuk issued a new appeal for Russia to halt all of its military movements in Crimea. Yatsenyuk also said Ukraine refused to respond with force to Russian "provocations."
Speaking during a televised cabinet meeting in Kyiv, Yatsenyuk said that "the inadequate presence of Russian troops on Ukrainian territory is a provocation, and Russian attempts to make Ukraine react with force have failed."
People hold signs reading "Crimea is Ukraine" during a rally on Independence Square in central Kyiv on March 1.
Foreign Minister Andriy Deshchytsya said Russia had declined to hold talks with Ukraine on an agreement guaranteeing the country's territorial integrity. Deshchytsya was quoted by Interfax news agency as saying the government was worried by Russia's refusal of talks.
With reporting by Reuters, AP, AFP, ITAR-TASS, Interfax, UNIAN, and RFE/RL's Ukrainian Service