(CNN) -- Russia rejected accusations that it is acting aggressively toward neighbor Ukraine, telling its Western critics Monday to put aside "geopolitical calculations" in favor of the interests of the people in the former Soviet republic.
Moscow has defended its parliament's approval of President Vladimir Putin's use of military force to protect its citizens in the Crimean Peninsula -- an autonomous region of eastern Ukraine with strong loyalty to Russia -- despite its G8 partners condemning its military buildup in the country and demanding that it withdraw
"I repeat: This is a matter of defending our citizens and our compatriots, of defending the most important human right -- the right to life," Russian Foreign Minister Sergey Lavrov said at a U.N. human rights meeting in Geneva, Switzerland.
"Those who attempt to interpret the situation as an act of aggression and threaten us with sanctions and boycotts -- these are the very same partners of ours who consistently have encouraged political forces close to them to deliver an ultimatum and refuse dialogue, to ignore the concerns of southern and eastern regions of Ukraine, which has ultimately polarized Ukrainian society."
He added that Moscow was calling "for a responsible approach, to put aside geopolitical calculations, and above all to put the interests of the Ukrainian people first." He accused Ukraine's new authorities -- in place since President Viktor Yanukovych was ousted last week -- of attacking minorities and violating human rights.
Separately, Russia's Finance Ministry said Monday that it would make a decision on financial aid to Crimea by the end of the day.
In Kiev, Ukrainian interim Prime Minister Arseniy Yatsenyuk, who has accused Moscow of declaring war, vowed that his West-leaning government would not give up the Crimean region.
"Nobody will give Crimea away. ... There are no grounds for the use of force against civilians and Ukrainians, and for the entry of the Russian military contingent," he said at a news conference. "Russia never had any grounds and never will."
Ukraine's shaky new government has mobilized troops and called up military reservists as officials say signs of Russian military intervention in Crimea are clear.
A senior U.S. administration official told CNN on Sunday that Russian forces "have complete operational control of the Crimean Peninsula." The official said the U.S. estimates there are 6,000 Russian ground and naval forces in the region.
"There is no question that they are in an occupation position -- flying in reinforcements and settling in," another senior administration official said.
Camouflaged and unidentified
Ukrainian border guards on Monday reported a buildup of armored vehicles on the Russian side of a narrow sea channel dividing Russia and Crimea, Reuters reported, citing a border guard spokesman.
He said that Russian ships had been moving in and around the port city of Sevastopol, where the Russian Black Sea Fleet has a base, and that Russian forces had blocked mobile telephone service in some areas. The buildup of Russian armor was near a ferry port on the Russian side of the Kerch Channel, opposite the Ukrainian city of Kerch.
Meanwhile, the Ukrainian State Border Security Service said there had been several attacks on border posts in eastern Crimea just along the border with Russia.
In a statement on its website, it said men, wearing unidentified camouflage uniforms, were carrying out the attacks, such as one on the Kerch border post, where doors and windows were broken and phone lines were destroyed late Sunday.
Also on Sunday night, armed men in unidentified camouflage uniforms tried to enter the arms depot in Ukraine's Belbek military base near Sevastopol, a Defense Ministry spokesman said.
Ukrainian forces at the base shot into the air to warn them off, but the unidentified men used sound grenades, and one of the Ukrainian commanders was wounded as a result, Vladislav Seleznev, the Ukrainian Defense Ministry spokesman in Crimea, told CNN.
The attackers gained access to the base, but Ukrainian troops retain control of the weapons depot and administration building. Seleznev added there have been negotiations.
Men dressed in both civilian and camouflage gear and wearing red armbands have been seen on the streets of the regional capital, Simferopol. The area has seen several pro-Russia demonstrations in the last few days, with crowds waving Russian flags and shouting "Thank you, Putin."
Navy defector seeks allies
Ten Ukrainian military and naval bases in Crimea are currently blocked by armed men, the newly appointed naval commander of Ukraine, Rear Admiral Serhei Gayduk, told a Ukrainian TV station by phone.
His predecessor, Denis Berezovsky, who on Sunday said he would not submit to orders from Kiev and defected, was said to have entered the Ukrainian naval base in Crimea on Monday under the protection of a group of Cossacks and tried to convince other Ukrainian officers to defect.
However, Gayduk was at the base and urged officers to maintain their allegiance to Ukraine, the Defense Ministry's Seleznev told CNN. Troops responded by singing the Ukrainian national anthem.
These scenes come after Putin secured permission from his parliament Saturday to use military force to protect Russian citizens in Ukraine and told U.S. President Barack Obama he had the right to defend Russian interests and nationals, spurning Western pleas not to intervene.
In a post on his official Facebook page Monday, Russian Prime Minister Dmitry Medvedev called Yanukovych's ouster a "seizure of power."
"Such a state of order will be extremely unstable," he said. "It will end with the new revolution. With new blood."
What is Russia's interest in Ukraine?
The tensions have worried the West, and on Sunday, Russia's G8 partners condemned Moscow's military buildup in Crimea. The world's seven major industrialized powers also suspended preparations for the G8 summit in Sochi, Russia, in June.
Their finance ministers announced some economic support for cash-strapped Ukraine, in a boost for the country's West-leaning new government.
"We are also committed to mobilize rapid technical assistance to support Ukraine in addressing its macroeconomic, regulatory, and anti-corruption challenges," G7 finance ministers said in a prepared statement, adding that an International Monetary Fund team was due to travel to Kiev this week.
U.S. Secretary of State John Kerry is also scheduled to travel to Kiev. He has condemned what he called Russia's "incredible act of aggression" and said several foreign powers are looking at economic consequences if Russia does not withdraw its forces.
British Foreign Secretary William Hague is currently in Kiev, where he visited the central Independence Square, cradle of the three-month protests that ousted Yanukovych, and lay flowers for those who died in clashes between demonstrators and riot police.
U.N. Secretary-General Ban Ki-moon has also dispatched an envoy. "It is now of the utmost importance to install calm and de-escalate tensions immediately through dialogue," he said at a news conference, adding that he would meet Lavrov later Monday.
He urged "that the Russian Federation refrain from any acts and rhetoric that can further escalate the situation and instead engage constructively and through peaceful means with Ukraine."
German Chancellor Angela Merkel's office said Putin had accepted a proposal to establish a "fact-finding mission" to Ukraine, possibly under the leadership of the Organization for Security and Co-operation in Europe, and to start a political dialogue.
East vs. West
Ukraine, a nation of 45 million people sandwiched between Europe and Russia's southwestern border, has been in chaos since Yanukovych was ousted on February 22 after bloody street protests that left dozens dead and hundreds wounded.
Anti-government demonstrations started in late November, when Yanukovych spurned a deal with the EU, favoring closer ties with Moscow instead.
Ukraine has faced a deepening split, with those in the west generally supporting the interim government and its European Union tilt, while many in the east prefer a Ukraine where Russia casts a long shadow.
Nowhere is that feeling more intense than in Crimea, the last big bastion of opposition to the new political leadership. Ukraine suspects Russia of fomenting tension in the autonomous region that might escalate into a bid for separation by its Russian majority.
Ukrainian leaders and commentators have compared events in Crimea to what happened in Georgia in 2008. Then, cross-border tensions with Russia exploded into a five-day conflict that saw Russian tanks and troops pour into the breakaway territories of South Ossetia and Abkhazia, as well as Georgian cities. Russia and Georgia each blamed the other for starting the conflict.
The crisis has hit Russian stock markets, with Moscow's main MICEX index opening about 8% lower Monday. The central bank hiked interest rates to 7% from 5.5%.